What is an SMTP server?

The acronym of SMTP is simple mail transfer protocol, which is the process behind the sending and receiving of email on the internet.

Have you ever taken your time to understand what happens after you send an email?  The steps of email delivery are similar to those of a standard mail, which is an organized system that looks after your envelope, and via some linked procedures, it drops your envelope to your intended recipient.

During the entire delivery process, your SMTP server operates as a computer running SMTP. Besides, your SMTP at the moment can be taken more or less as a postman.  After the messages have been received, they are directed to the server. The server will then take care of them, by solidly delivering emails to the intended recipients.

Normally, the whole process involved after you send an email can simply be; you send your email to and SMTP server, then from the SMTP server to the internet, from the web the email is taken to a POP/ IMAP server, and finally to the user.   Right from you to the POP/IMAP server, the email is under the control of an SMTP, then under POP.

Here is a summary of the process:

  • You send an email using your mail client or webmail using your email address, to the intended recipient. The webmail or client is referred as the message user agent, abbreviated as MUA.
  • The message is sent through port 25 to the SMTP server, for example, email. Website.com. The SMTP server is provided to your customer after you set it up, and it acts as a message transfer agent, which can be abbreviated as MTA. The client and the server initiate a conversation, and the server looks at all the data regarding the transmission of messages such as domain, sender, recipient and others.  Only message transmission is defined by SMTP language but not the content of its body.
  • If your recipient has an account with a domain linked directly to the server, then delivery of the email will be done immediately. If it is not connected, the SMTP directs to another incoming server, which is near the recipient.  These passenger servers are known as relays. In this case, the website server is connecting to the domain server, which receives and keeps.
  • If the recipient server is busy or down, the SMTP host leaves the message to a backup server if both are not available, the email gets queued, and delivery retried repeatedly. The message is then returned as undelivered after the trial period.
  • However, if there is no issue with delivery, the final stage is regulated by the POP, which is a protocol which takes the email from the receiving server and delivers it to the recipient’s inbox.

However, it is important to note that SMTPs you use to send regular emails such as those linked to providers like Gmail, Yahoo, and Hotmail get shared among users. Also, their basis is non-dedicated IPs, meaning you can finally depend on an IP that gets used by spammers, hence affecting the proper delivery of your messages.  Besides, there are limited numbers of emails to send to current providers.