SMTP, Simple Mail Transfer Protocol, is a protocol or set of communication rules used by email servers to send and receive emails.
If you use transactional emails on your website or perform any email marketing efforts, you may have heard the term SMTP and wondered, what is SMTP and what does it have to do with me?
This protocol is of vital importance for marketers as it directly impacts the emails they send to their customers and their deliverability.
Although SMTP is a fairly technical topic, and all of this may sound a bit like india phone number list an engineer's idea, don't worry, this guide will teach you everything you need to know, but from a less technical point of view so that you can better understand how SMTP can impact your marketing strategy.
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All the faces of SMTP
While the acronym SMTP actually refers to the communication protocol used by email servers, it is also used as:
SMTP Relay
SMTP Server
Read on to learn the differences between the three.
SMTP Protocol
SMTP primarily refers to the set of rules that mail servers use to transfer electronic messages over the Internet.
To be more exact, the protocol works as follows:
The sender and recipient of the message are specified
A request is sent to both the sender and recipient to verify that both addresses exist.
The message is transferred from the sender to the recipient
Steps to send messages via SMTP protocol (for those who really want to learn)
If you're a marketing expert, you may not be interested in the details of how this protocol works, but if you want to shine at your next team meeting, here's a more detailed rundown of the process:
A few important acronyms:
MUA (Mail User Agent) - Email client (e.g. Gmail, Yahoo, Outlook)
MSA (Mail Submission Agent): Computer software running on an SMTP server, receives messages from an MUA and checks them for errors before passing them on to an MTA.
MTA (Mail Transfer Agent): software that checks the MX record of the recipient's domain to decide how to proceed with the transfer of the message (whether to send it to another MTA or to an MDA)
MX (Mail Exchanger Record) Record: This is a record that specifies from which server the recipient's MUA can retrieve the message.
MDA (Mail Delivery Agent): software that stores messages for retrieval by MUAs
These are the 6 main steps that make up the SMTP transfer process:
The email is sent by an MUA to the MSA of a mail server
The message is transferred to the server's MTA (the MTA and MSA are usually hosted on the same SMTP server)
The MTA verifies the MX record of the recipient's domain and transfers the message to another MTA (this step may occur several times until the correct receiving server receives the message)
The message is transferred to the MDA, which saves the messages in the appropriate format for retrieval by the MUA.
The MUA requests the message from the MDA (usually with POP3 or IMAP)
The message is sent to the recipient MUA's inbox
To give you a clearer picture, here is a graphic showing the process in action:
SMTP server
SMTP Relay
You've probably come across the term SMTP relay more than once in your email marketing research. It's a more technical term that refers to the act of transferring an email to the appropriate destination server.
In practice, however, the term SMTP relay most often refers to the actual servers through which emails pass before reaching their destination, such as a mail processing and distribution center. In this case, you can think of "SMTP relay" as a synonym for SMTP server.
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