If you use transactional emails on your website or do any kind of email marketing, you’ve probably heard the term SMTP — but you might be wondering, what is SMTP and what does it have to do with me?
SMTP, which stands for Simple Mail Transfer Protocol, is a communication protocol, or set of rules, used by mail servers to efficiently send and receive electronic messages (emails) over the internet.
This protocol is important for marketers because it directly impacts the emails you send and their deliverability.
If that all sounds a little daunting, don’t worry — although SMTP is a pretty technical subject, this guide will teach you what you need to know from a less technical standpoint so you can better understand how it impacts your email marketing.
The many faces of SMTP
While the acronym SMTP actually refers to the communication protocol used by mail servers, it has also been used interchangeably with:
- SMTP relay
- SMTP server
Read on to learn the differences between the three.
As we mentioned above, SMTP primarily refers to the set of rules that mail servers use to transfer electronic messages over the internet.
More concretely, the protocol works like this:
- The sender and recipient of the message are specified
- A request is sent to both the sender and recipient to verify they exist
- The message is transferred from the sender to the recipient
Steps for transferring messages over SMTP (for those who really want to know)
If you’re a marketer, you might not be interested in the minute details of how this protocol works, but just in case you want to shine in your next meeting with your tech team, here is a more detailed look at the process:
A few important acronyms:
- MUA (Mail User Agent) – Email client (e.g. Gmail, Yahoo, Outlook)
- MSA (Mail Submission Agent) – Computer software run on an SMTP server that receives messages from a MUA and checks for any errors before transferring to a MTA.
- MTA (Mail Transfer Agent) – Software that checks recipient domain’s MX record to decide how to continue transferring the message (either to another MTA, or an MDA)
- MX Record (Mail Exchanger Record) – Is a resource record that specifies from which server the recipient MUA for that domain can retrieve the message.
- MDA (Mail Delivery Agent) – Software that stores messages for batch retrieval for MUAs
Now that you’ve got the SMTP vocabulary down, it’s time to talk about how they all fit together to create the protocol for transferring electronic messages over the internet.
Here are the 6 main steps that comprise the transfer process for SMTP:
- Email is submitted by a MUA to a mail server’s MSA
- The message is transferred to the server’s MTA (the MTA and MSA are usually hosted on the same SMTP server)
- The MTA checks the MX record of the recipient domain and transfers the message to another MTA (this step can occur multiple times until the message is received by the proper receiving server)
- The message is handed off to the MDA, which saves messages in the proper format for retrieval by the receiving MUA
- The receiving MUA requests the message from the MDA (usually with POP3 or IMAP)
- The message is delivered to the receiving MUA‘s inbox
To give you a more clear visual — here is a graphic that shows the process in action:
In your reading on email marketing, you might have also come across the term SMTP relay — a more technical term that refers to the act of transferring an email to the proper destination server.
In practice though, the term SMTP relay more often refers to the actual servers through which emails pass before arriving at their destination like a mail processing and distribution center. In this case, you can think of “SMTP relay” as a synonym for SMTP server.
An SMTP server is simply the server that receives, handles, transfers, or stores messages to according to the rules of SMTP (the communication protocol).
SMTP Servers and Deliverability
Now that you have a better understanding of what SMTP means, let’s get to what you’re really interested in: email deliverability.
The SMTP server that you use to send out your emails is associated with a specific IP address. This address is directly tied to your deliverability because it is this address that ISPs use to check your sender reputation.
Due to the nature of their service, the SMTP servers set up by classic email providers (Gmail, Yahoo, Outlook, etc.) for sending personal emails are not adapted to handle the sending of bulk emails.
The reason for this is that their IPs are not closely monitored, meaning you could be sending emails from the same server as a known spammer. So, if you send bulk emails through classic email providers like this, you are guaranteed to end up in the spam folder.
What is the solution to this SMTP server problem?
If you want to achieve the best possible deliverability for your bulk emails, you’ll need to use a professional SMTP relay service that has been set up expressly for the purpose of delivering bulk emails.
At SendinBlue, all of our servers are built on a solid and reliable infrastructure that enables us to send millions of emails every day for our clients.
Because we maintain strict control over all of our IP addresses, users can benefit from excellent deliverability for both marketing emails and transactional emails.
If you require even more control over your sender reputation, SendinBlue also offers dedicated IP addresses to our higher-volume senders. This means you don’t have to worry about the sending behavior of anyone else affecting your deliverability.
Want to reach your clients’ inboxes without any problems? Create a SendinBlue account today and enjoy sending up to 9,000 emails per month for free!
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