Are your emails going to SPAM? Don’t worry, It's OK.
It is very common for emails to go land in the spam folder for a new sender with a new SMTP server (Email Server), new IP & Domain.
Even if all technical aspects such as SPF, DKIM, DMARC, RDNS, No Blacklists, and 10/10 Score on Mail-Tester.com are in place, your emails may land in spam.
When you build a New SMTP Server with a new IP Address, or when you subscribe to an SMTP Service Like Amazon SES with a Dedicated IP, and before You can Start Sending any Email Marketing Campaigns, you have to warmup your IP Address.
Also, you need to warm it up if you left your IP without sending any email for more than 30 days or so.
So, SMTP warmup is somehow a continuous process.
What is Warming Up IP?
When you have a new Brand IP Address for your SMTP, this IP will have no Reputation on the internet, and ISPs (internet service providers) don't know this IP. So, IP warmup is the practice of building your reputation on the internet by gradually increasing the volume of emails sent with your IP address according to a predetermined schedule.
When an ISP notices an email suddenly coming from a new IP address, they will immediately begin evaluating the traffic coming from that IP.
Since ISPs treat email volume as a key in determining spam, it is best to start sending a low email volume, then increasing up your way up to more significant amounts.
This gives the email providers a chance to carefully observe and analyze your sending habits and volumes and record how your recipients engage with your email.
In general, Warming up takes between 2-10 Weeks according to your scenario and the number of emails you want to send per day.
How do ISPs evaluate your emails and Reputation?
When you start the warming up process, ISPs will Evaluate your Reputation according to three Main Factors:
- Bounce Rate: When you send an email campaign, you need to ensure that your emails are valid emails, High bounce rate will destroy your reputation.
- Spam Traps: Even a very low percentage of spam traps can blacklist you!
- Spammy Content: Your message content is essential. ISPs will check if you are using any spammy keywords or blacklisted links.
- User Interaction: How Recipients are interacting with your emails, if they are reporting you as spam, then this is a real problem!
Warming Up IP in Action (Examples)
Ok, now after we have the big picture warming up SMTP, let’s go with some examples and real scenarios and understand how the operation works:
Please note: These sample schedules are intended to be a suggestion only. Every sender is different.
1. 1000 Emails Per Day
This is not a big deal, you start by sending 14 emails the first day, then increase gradually to reach 1K in about 10-15 days. The schedule is described in the following table:
|Day||No. Of Emails||Increment Emails Per Day|
2. 10K Emails Per Day
Now, in this scenario, we do the same thing, but with a more extended schedule, check the following table:
|Day||No. Of Emails||Increment Emails Per Day|
3. 50K Emails Per Day
Now 50K per day is considered somehow a big number.
As a little advice, and to make things easier, always split large volume warmup campaigns into smaller ones, like in our case, we split it into three schedules:
- Reach 10K emails.
- Reach 30K emails.
- Reach 50K emails.
You may say, this will make the warmup schedule longer, maybe yes, but in our experience in this way, you can monitor and manage your warming-up campaigns easily and get better results.
So, if you were warming to 10K, the number of emails would be less, and you can see and monitor the user interaction and bounce rate on a smaller amount of emails, which will make the picture clearer.
I hope you got the point.
Free Warmup Tool
Warmup Schedule Generator
Then, Select Your Email List Size, and Click Generate! And See the Magic
Email Volume and Timeline
For IP warmup, the warmup schedule, and the sending volume is different for all senders.
The number of emails you send depends on your own total email volume, some may require to send 100 emails per day, and others may need 1M per day!
But in any case, you must send enough emails at enough frequency so that your email reputation can be tracked.
Also, you have to know something very important, most reputation systems only store data for 30 days, so you should not go 30 days or more without sending on an IP. If you do, then you will need to warm it up again. This is why we said above that warming up an IP is a continuous process.
Transaction VS Marketing Emails
If you want to use your SMTP server to send Transactional Emails (Password resets, invoices, welcome emails…). In this case, you may be an established business or a new business.
If you are already sending a lot of emails, and you decide to move to an ESP for the first with dedicated IP or build your own SMTP, you should migrate you're sending a little bit at a time.
One way to do this is to split your traffic and move small portions of it to the new IP over time.
Alternatively, if you are already maintaining multiple mail servers, you can move your servers over to your new IP one at a time.
Typically, the organic growth of your business will, by its nature, create an ideal ramp. Since transactional email is usually dependent on the number of users you have, the growth in your customer base will create a nice, comfortable growth curve in your email volume. So you will not worry about warming up in this case.
But still, it's important to monitor your reputation and your system to see how it's performing. (We will talk about monitoring reputation later)
Email Marketing Campaigns
The Simplest Approach is to estimate your total monthly email volume and divide that number by 30.
Then, try to spread your sending evenly over the first 30 days, based on that calculation. For example: if you will send 90,000 emails/month, you should start off sending 3,000 per day over the first month and so on.
Maintain Warmup across ALL ISPs
It’s important to remember that you must maintain a steady volume during the entire warmup period for each ISP.
So remember to split up your warmup schedule so each ISP is receiving a comparable amount of mail each day – don’t warmup Gmail on Monday, Yahoo! on Tuesday, etc. – evenly disperse your mail to each ISP on each day of warmup.)
If not, your sending activity looks sporadic and you won’t be able to build a solid reputation.
Just mix things up! Don't send to one ISP at a time.
Warming up IP Tips:
There are some crucial tips that you have to Follow while warming up IP:
- Don’t ever start before you get a High sending score: Ensure this by configuring SPF, DKIM, rDNS, and other Technical Details.
- Don’t ever send promotional emails in the warmup period. You need the highest engagement rates, so send transactional emails or maybe some valuable info.
- Mail only to your top active subscribers first. Ensure almost 0% bounce rates.
- Don’t rotate or switch IPs during warmup. Rotation is a sign of spam.
- In your emails, add a clear link for people to unsubscribe.
- Add an Email Signature that makes your emails look trusted.
- Mix your campaigns with premium SMTP services – this will give better user interaction and domain reputation.
- Join Newsletters. This will make a lot of emails come to your inbox and give you a Higher domain reputation.
- Send to your friend’s list and ask them to report you as non-spam and tell them to reply.
- Try your best to build an audience and warmup to that audience. In this way, you will achieve the best user interaction and will make the “warming up process” a lot easier.
- Monitor your campaigns accurately, and be sure to keep your bounce rate below 2% by validating your emails (You can use our service to validate the emails – Bulk Email Verification)
How to Monitor IP Reputation?
So, you need to monitor your Bounce rate, user feedback, and reputation score.
Some Services Like Amazon SES, and Sparkpost has a built-in reputation system that shows your Bounce Rate and User Interaction.
If you are using a Custom SMTP as we explained in How To Set Up SMTP Server With Postal (Step By Step Guide) or whatever SMTP you are using.
In some cases, you will be able to monitor bounces and user feedback through the mailing system like in MailWizz. You can also monitor open, unsubscribe, and open rates. This will give you an indication of how users are interacting with your messages.
Having the right tools for checking the IP reputation is halfway to success. Here are some tools and
services you can use:
- senderscore.org by Return Path. The score ranks from 0 to 100, 100 being the best. It tells you how you're performing. Typically it's recommended that you maintain your sender score of 90 or better.
- talosintelligence.com by Cisco. It tells you how your reputation is across all the network providers Cisco manages. The reputation score is grouped into Good, Neutral, and Poor.
- postmaster.live.com Microsoft's Smart Network Data Services gives you information about the traffic originating from your IP address such as the volume of sent emails, complaint rates, and spam trap
- postmaster.google.com Gives access to your domain's data on Google Search Console.
- postmaster.aol.com Check your IP reputation and rates it as “bad”, “neutral”, and “good”.
IP warmup is the act of sending emails gradually to build a good reputation and reach the recipient’s inbox. So, be careful, and follow the guidelines and tips listed above, to achieve the best results.
Good Luck, if you have questions or clarifications, you can comment below, or open a question on Sapnaaz Forum.
Hope You All The Best!
Postal is a fully-featured open-source mail delivery platform for incoming & outgoing e-mail and gives you all the tools and features needed to build a full mailing system for your business.
What is the SMTP Server?
We have described it in detail about this in our another blog “What is a SMTP Server?“. But if you want know it in brief, here it is:
SMTP is that thing that allows you to send emails over the internet.
SMTP stands for “Simple Mail Transfer Protocol”. It's a Concept in Networking that you don't have to worry about.
Just Know that SMTP is the technical thing that is responsible for delivering emails over the internet.
What do we mean by Sending Unlimited Emails?
When we say unlimited emails, this means that we can send unlimited emails from our server, there are no restrictions by companies or monthly plans to buy or so.
It's your server, you can send as much as your server can handle in terms of resources. So when you have more CPU and RAM, you can send more emails and so on.
Let's Start The SMTP Server Setup
Ok, let's start the real work! But, before we start, you need to know what is required.
Requirements to Setup SMTP Server.
In order to Build and Setup an SMTP Server, you will mainly need two things:
1. Domain name
When you send emails, you will be sending from an email address like this one:
So if you don't have a domain yet, go and get one now in order to continue the setup.
How to get a domain? Simply you buy one! And it costs around 10$/year, so it's not that big deal!
Here in this course, we will be using Namecheap to get my domain, but you can use any other service if you want, all work in the same way, and if you need any help, we will be here 🙂.
Got a Domain? Great! ✔️ Let's continue.
2. VPS Server with Port 25 opened.
What is a VPS server?
If you don't know what is a VPS server, simply it's a computer (a server) running in the cloud that you buy from a Web Hosting or Cloud Services company. And it's publicly accessible with a Public IP.
A VPS can be used to host your websites with higher performance and can be used to run a machine 24/7 in the cloud to do any task you want.
Port 25 open??
We mentioned that the VPS must have port 25 opened, what does this mean?
We don't want to bother your head dealing with technical stuff but, in short, any network service or software uses a certain port to communicate over the internet or network. For example:
- Connecting remotely to another Windows Machine using RDP software works over port 3389.
- SQL database systems like MYSQL on our computer works over port 3306.
- Connecting to a Linux machine remotely to manage it with SSH, uses port 22.
- When you surf the web and open websites, we use port 80. and so on.
By default, all servers and computers have a firewall running which blocks all ports except the ones you want. So, to use a certain service, we need to open that port in the firewall.
What you have to know also, that ports can be blocked and opened in two ways, incoming and outgoing, the following diagram will make things clearer:
When you get a VPS server, just make sure that the company allows Port 25 and don't block it, because some companies do this to protect from spammers.
Here is a list of some companies that allows port 25 by default:
Are there any other Companies? Yes, you can contact the support of any company you want and ask if they block any ports by default. If not, then perfect, you can go with it.
Feel free to use any VPS company you want, It's up to you!
You can also sign up on DigitalOcean through this coupon link to get free $100 to test everything for free.
Or start with Contabo which we think is the cheapest VPS service that you can use, we have 2 servers configured with Contabo.
- Ubuntu 22.04 or 20.04 or 18.04 x64 as your operating system
- You can start with 1 CPU/2 GB RAM (And resize later).
Got your VPS? Great! ✔️ Let's continue.
VPS Server basic configuration
Now we have our new Ubuntu VPS server, let’s prepare it out for setup.
- Press Win + R on your keyboard.
- Type cmd, and press Enter. A new window will open.
- In the window, type ssh username@ip-address (replace username with the username of your server and ip-address with the IP address of your server)
First, check your hostname:
If you don’t see a form of ANYTING.YOURDOMAIN.COM, then you need to change the hostname using the following command:
sudo hostname server.domain.com
Where the host is anything you want. Our domain for this tutorial is sapnaaz.com, so the command will look like this:
sudo hostname postal.sapnaaz.com
Map your domain name
Host: postal (Whatever you have chosen) Points To: YOUR_SERVER_IP
Done? ✔️ Let's continue.
Install Postal Mail Server on Ubuntu 22.04/20.04/18.04
The installation of Postal Mail Server on Ubuntu is not as complicated as others say. By sparing some minutes and following below few steps, you should have Postal Mail Server running on Ubuntu 22.04/20.04/18.04 server.
Step 1: Update your system
Like all other installations, we start the installation by ensuring our system is updated.
sudo apt update sudo apt -y upgrade
Perform a reboot if it is required:
[ -f /var/run/reboot-required ] && sudo reboot -f
Then install git once the system is up
sudo apt -y install git curl jq
Step 2: Install Docker & Docker Compose
Import Docker repository GPG key:
curl -fsSL https://download.docker.com/linux/ubuntu/gpg | sudo gpg --dearmor -o /etc/apt/trusted.gpg.d/docker-archive-keyring.gpg
With GPG key imported you can add Docker repository to your Ubuntu system.
sudo add-apt-repository "deb [arch=amd64] https://download.docker.com/linux/ubuntu $(lsb_release -cs) stable"
Finally install Docker CE on Ubuntu 22.04/20.04/18.04:
sudo apt update sudo apt install docker-ce docker-ce-cli containerd.io
Add your user account to docker group.
sudo usermod -aG docker $USER newgrp docker
Confirm successful installation by checking Docker version
$ docker version Client: Docker Engine - Community Version: 20.10.16 API version: 1.41 Go version: go1.17.10 Git commit: aa7e414 Built: Thu May 12 09:18:18 2022 OS/Arch: linux/amd64 Context: default Experimental: true Server: Docker Engine - Community Engine: Version: 20.10.16 API version: 1.41 (minimum version 1.12) Go version: go1.17.10 Git commit: f756502 Built: Thu May 12 09:16:22 2022 OS/Arch: linux/amd64 Experimental: false containerd: Version: 1.6.4 GitCommit: 212e8b6fa2f44b9c21b2798135fc6fb7c53efc16 runc: Version: 1.1.1 GitCommit: v1.1.1-0-g52de29d docker-init: Version: 0.19.0 GitCommit: de40ad0
Download the latest Compose
curl -s https://api.github.com/repos/docker/compose/releases/latest | grep browser_download_url | grep docker-compose-linux-x86_64 | cut -d '"' -f 4 | wget -qi -
Make the binary file executable.
chmod +x docker-compose-linux-x86_64
Move the file to your PATH.
sudo mv docker-compose-linux-x86_64 /usr/local/bin/docker-compose
$ docker-compose version Docker Compose version v2.6.1
Step 3: Install MySQL / MariaDB database server
The other requirement of Postal Mail server is a database server.
Now, you can install MariaDB in the docker container.
docker run -d \ --name postal-mariadb \ -p 127.0.0.1:3306:3306 \ --restart always \ -e MARIADB_DATABASE=postal \ -e MARIADB_ROOT_PASSWORD=postalpassword \ mariadb
Step 4: Install and Configure RabbitMQ
Postal uses RabbitMQ for queueing. RabbitMQ is necessary to process messages and distribute the loads
To install it, run the following commands
docker run -d \ --name postal-rabbitmq \ -p 127.0.0.1:5672:5672 \ --restart always \ -e RABBITMQ_DEFAULT_USER=postal \ -e RABBITMQ_DEFAULT_PASS=password \ -e RABBITMQ_DEFAULT_VHOST=postalvhost \ rabbitmq:3.8
Now we have installed all the prerequisite packages, it’s time to install Postal
Step 5: Install and Configure Postal on Ubuntu 22.04/20.04/18.04
Cloning the Postal repository
sudo git clone https://postalserver.io/start/install /opt/postal/install
Create a symlink for Postal binary
sudo ln -s /opt/postal/install/bin/postal /usr/bin/postal
You’ll need these records for accessing the API, management interface & SMTP server.
You can configure a global SPF record for your mail server which means domains don’t need to each individually reference your server IPs. This allows you to make changes in the future.
|spf.postal.yourdomain.com||TXT||v=spf1 ip4:Your_Server_IP ~all|
If you wish to receive an incoming e-mail by forwarding messages directly to routes in Postal, you’ll need to configure a domain for this just to point to your server using an MX record.
|rp.postal.yourdomain.com||TXT||v=spf1 a mx include:spf.rp.postal.yourdomain.com ~all|
Run the command below and replace postal.yourdomain.com with the actual hostname you want to access your Postal web interface at.
$ sudo postal bootstrap postal.example.com Latest version is: 2.1.1 => Creating /opt/postal/config/postal.yml => Creating /opt/postal/config/Caddyfile => Creating signing private key
This will generate three files in /opt/postal/config.
- postal.yml is the main postal configuration file
- signing.key is the private key used to sign various things in Postal
- Caddyfile is the configuration for the Caddy webserver
Open Postal configuration file.
sudo vim /opt/postal/config/postal.yml
At the minimum, have the following settings:
web: # The host that the management interface will be available on host: postal.yourdomain.com # The protocol that requests to the management interface should happen on protocol: https main_db: # Specify the connection details for your MySQL database host: localhost username: root password: postalpassword database: postal message_db: # Specify the connection details for your MySQL server that will be house the # message databases for mail servers. host: localhost username: root password: postalpassword prefix: postal rabbitmq: # Specify the connection details for your RabbitMQ server. host: 127.0.0.1 username: postal password: password vhost: postalvhost dns: # Specifies the DNS record that you have configured. Refer to the documentation at # https://github.com/atech/postal/wiki/Domains-&-DNS-Configuration for further # information about these. mx_records: - mx.postal.yourdomain.com smtp_server_hostname: postal.yourdomain.com spf_include: spf.postal.yourdomain.com return_path: rp.postal.yourdomain.com route_domain: routes.postal.yourdomain.com track_domain: track.postal.yourdomain.com smtp: # Specify an SMTP server that can be used to send messages from the Postal management # system to users. You can configure this to use a Postal mail server once the # your installation has been set up. host: 127.0.0.1 port: 2525 username: # Complete when Postal is running and you can password: # generate the credentials within the interface. from_name: Postal from_address: firstname.lastname@example.org
Edit the file to fit your Postal settings.
When done Initialize database by adding all the appropriate table:
$ sudo postal initialize [+] Running 5/5 ⠿ smtp Pulled 0.5s ⠿ cron Pulled 0.5s ⠿ requeuer Pulled 0.5s ⠿ worker Pulled 0.5s ⠿ web Pulled 0.5s Initializing database ......
Create your initial admin user
Add your Email, Name & Suitable Password (Remember this email and password as this will be required to login to postal)
$ sudo postal make-user Postal User Creator Enter the information required to create a new Postal user. This tool is usually only used to create your initial admin user. E-Mail Address : email@example.com First Name : Admin Last Name : User Initial Password: : ******** User has been created with e-mail address firstname.lastname@example.org
Starting the application
Run the following command to start the Postal application
$ sudo postal start [+] Running 5/5 ⠿ Container postal-cron-1 Started 0.4s ⠿ Container postal-web-1 Started 0.2s ⠿ Container postal-requeuer-1 Started 0.3s ⠿ Container postal-smtp-1 Started 0.3s ⠿ Container postal-worker-1 Started 0.3s
This will run a number of containers on your machine.
You can look at the status at any time using:
$ sudo postal status NAME COMMAND SERVICE STATUS PORTS postal-cron-1 "/docker-entrypoint.…" cron running postal-requeuer-1 "/docker-entrypoint.…" requeuer running postal-smtp-1 "/docker-entrypoint.…" smtp running postal-web-1 "/docker-entrypoint.…" web running postal-worker-1 "/docker-entrypoint.…" worker running
Step 6: Configuring Caddy Web Server
A web proxy is required for all web traffic and SSL termination. There are many options for Proxy – Nginx, Apache, HAProxy, e.t.c. In this guide, we’re going to use Caddy.
We can run Caddy web server using Docker:
docker run -d \ --name postal-caddy \ --restart always \ --network host \ -v /opt/postal/config/Caddyfile:/etc/caddy/Caddyfile \ -v /opt/postal/caddy-data:/data \ caddy
Check it’s running:
$ docker ps CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES 67461a34ae39 caddy "caddy run --config …" 20 seconds ago Up 20 seconds postal-caddy 1bc1bac79c15 ghcr.io/postalserver/postal:2.1.1 "/docker-entrypoint.…" About a minute ago Up About a minute postal-smtp-1 c5a04cea4211 ghcr.io/postalserver/postal:2.1.1 "/docker-entrypoint.…" About a minute ago Up About a minute postal-worker-1 e188ee4c2844 ghcr.io/postalserver/postal:2.1.1 "/docker-entrypoint.…" About a minute ago Up About a minute postal-requeuer-1 d7335cd48fa1 ghcr.io/postalserver/postal:2.1.1 "/docker-entrypoint.…" About a minute ago Up About a minute postal-web-1 c4b1cc7a852e ghcr.io/postalserver/postal:2.1.1 "/docker-entrypoint.…" About a minute ago Up About a minute postal-cron-1
Once this has started, Caddy will issue an SSL certificate for your domain and you’ll be able to immediately access the Postal web interface and login with the user you created in one of the previous steps.
Once you have installed Postal, you can upgrade to the latest release it by running this command:
$ sudo postal upgrade warning: redirecting to https://github.com/postalserver/install/ From https://postalserver.io/start/install * branch main -> FETCH_HEAD Already up to date. No version specified, using latest available version... Upgrading to 2.1.1 [+] Running 5/5 ⠿ worker Pulled 1.5s ⠿ cron Pulled 0.5s ⠿ web Pulled 0.4s ⠿ smtp Pulled 0.5s ⠿ requeuer Pulled 0.5s Migrating database [+] Running 5/0 ⠿ Container postal-worker-1 Running 0.0s ⠿ Container postal-web-1 Running 0.0s ⠿ Container postal-smtp-1 Running 0.0s ⠿ Container postal-requeuer-1 Running 0.0s ⠿ Container postal-cron-1 Running 0.0s
Step 7: Access Postal Admin Web Dashboard
Access Postal Administration page on https://postal.yourdomain.com
You should see Let’s Encrypt SSL certificate in place if your installation was successful and login with admin user email created earlier.
You’ll get a dashboard which looks like this:
Create your first organization
Provision mail server to start sending and receiving messages using Postal.
Give your mail server a name and choose live mode.
With the basic configurations required you can now use Postal email delivery software solution.
Refer to the Postal Administration guide for further configurations.
Congratulations! You have completed setting up your own Free SMTP Server using Postal. But before you start sending emails, you have to understand some crucial concepts and follow up on the guidelines to get the best delivery rates and reach the inbox!
- Warming Up your SMTP server – We will be updating a blog about this very soon.
- rDNS (Reverse DNS)
- DMARC (Domain-based Message Authentication, Reporting & Conformance)
- MX Record
- Avoid Spam Factors – IP Reputation, SPF, DKIM, DMARC, Message Body, Email List health.
Email is among the widely used communication channel, and most internet system uses Simple Mail Transfer Protocol SMTP to transfer email from their server to the recipient’s server.
It’s a standard communication protocol used by mail servers and other message transfer agents and can impact the deliverability of your campaigns.
What is the Simple Mail Transfer Protocol (SMTP)?
The Simple Mail Transfer Protocol (SMTP) is a technical standard for transmitting electronic mail (email) over a network. Like other networking protocols, SMTP allows computers and servers to exchange data regardless of their underlying hardware or software. Just as the use of a standardized form of addressing an envelope allows the postal service to operate, SMTP standardizes the way email travels from sender to recipient, making widespread email delivery possible.
SMTP is a mail delivery protocol, not a mail retrieval protocol. A postal service delivers mail to a mailbox, but the recipient still has to retrieve the mail from the mailbox. Similarly, SMTP delivers an email to an email provider's mail server, but separate protocols are used to retrieve that email from the mail server so the recipient can read it.
What is a protocol?
A protocol consists of a set of rules and procedures which govern the exchange of data between two or more devices. Protocols define how data transmission will occur between electronic devices such as computers. They set the standard procedures for communication and the exchange of information.
The International Organization for Standardization established the Open Systems Interconnection (OSI). One such widely used Internet protocol lays down the standard for communication over different networks. The model divides the process of data transmission into a series of seven layers.
Important internet protocols are TCP/IP, HTTPS, DNS, and SMTP.
What is an SMTP server?
An SMTP server is a mail server that can send and receive emails using the SMTP protocol. Email clients connect directly with the email provider's SMTP server to begin sending an email. Several different software programs run on an SMTP server:
- Mail submission agent (MSA): The MSA receives emails from the email client.
- Mail transfer agent (MTA): The MTA transfers emails to the next server in the delivery chain. As described above, it may query the DNS to find the recipient domain's mail exchange (MX) DNS record if necessary.
- Mail delivery agent (MDA): The MDA receives emails from MTAs and stores them in the recipient's email inbox.
Common SMTP server providers & settings
|SMTP Provider||URL||SMTP Settings|
How does the SMTP work?
The Transmission Control Protocol (TCP) is the primary connection for communication between the mail sender and the mail receiver. In SMTP, the mail sender sends the data in command strings over this reliable ordered data stream channel.
The SMTP client, the initiating agent, sender, or transmitter, initiates the communication session. It issues the command strings and opens the session for corresponding responses from the SMTP server, which involves the listening agent or receiver. Zero or more SMTP transactions may be there in a course.
Usually, an SMTP email transaction follows four command or reply sequences:
It tells the email server that the client wants to start the mail transaction. The client mentions its domain name after this command.
It lays down the bounce address/return address, defining the return or reverse paths.
It specifies the recipient of the message. The sender’s envelope contains the addresses of the recipients, to which the RCPT command can be issued multiple times for each recipient.
It shows where the content of the message starts, as opposed to its envelope. An empty line separates the message header and body in the message’s text.
DATA is not just one command but a group of commands in which a server has to reply twice
- First, the server acknowledges the message and replies with its readiness to take the message.
- Then after completing the end-of-data sequence, it either accepts or rejects the entire message.
Apart from the reply of the DATA command, the server can reply in a positive way (2xx reply codes) or a negative way.
The negative responses can further be permanent (5xx codes) or transient (4xx codes).
If a server sends ‘reject,’ then it is a permanent failure, and the client needs to send a bounce message to the respective server. On the other side, a ‘drop’ is a positive reply in which the message is discarded instead of delivered.
What is an SMTP envelope?
The SMTP “envelope” is the set of information that the email client sends to the mail server about where the email comes from and where it is going. The SMTP envelope is distinct from the email header and body and is not visible to the email recipient.
What port does SMTP use?
In networking, a port is a virtual point where network data is received; think of it as the apartment number in the address of a piece of mail. Ports help computers sort networking data to the correct applications. Network security measures like firewalls can block unnecessary ports to prevent the sending and receiving of malicious data.
- Port 25 is most used for connections between SMTP servers. Firewalls for end-user networks often block this port today, since spammers try to abuse it to send large amounts of spam.
- Port 465 was once designated for use by SMTP with Secure Sockets Layer (SSL) encryption. But SSL was replaced by Transport Layer Security (TLS), and modern email systems, therefore, do not use this port. It only appears in legacy (outdated) systems.
- Port 587 is now the default port for email submission. SMTP communications via this port use TLS encryption.
- Port 2525 is not officially associated with SMTP, but some email services offer SMTP delivery over this port in case the above ports are blocked.
Difference between SMTP, IMAP, & POP3
The Internet Message Access Protocol (IMAP) and Post Office Protocol (POP) are used to deliver the email to its final destination. The email client has to retrieve the email from the final mail server in the chain to display the email to the user. The client uses IMAP or POP instead of SMTP for this purpose.
To understand the difference between SMTP and IMAP/POP, consider the difference between a plank of wood and a rope. A length of wood can be used to push something forward, but not pull it in. A rope can pull an item, but cannot push it. Similarly, SMTP “pushes” email to a mail server, but IMAP and POP “pull” it the rest of the way to the user's application.
What is Extended SMTP (ESMTP)?
Extended Simple Mail Transfer Protocol (ESMTP) is a version of the protocol that expands upon its original capabilities, enabling the sending of email attachments, the use of TLS, and other capabilities. Almost all email clients and email services use ESMTP, not basic SMTP.
ESMTP has some additional commands, including “EHLO”, an “extended hello” message that enables the use of ESMTP at the start of the connection.
SMTPs are essential for sending and receiving emails. However, as an email marketer, you need to choose and configure the SMTP service providers that suit your requirements.
At Sapnaaz, we provide easy SMTP setup and integration with any SMTP servers you might like to send your email marketing campaigns. Feel free to reach out to the Sapnaaz team to learn more or check out our SMTP setup service page.