Working of receiving mail server

Question

Dear, I torn my hair since last 7-8 days to know the working of receiving mail server. The word "Receiving Mail Server" might sound confusing to you in the first instance. So let me first make you clear on that.

Complete Mail service works as follows:

1. We send email using a MTA (mail transfer agent) like "sendmail" on Linux or "Outlook" on windows.

2. Both these MTA deliver email to the SMTP server, which further delivers the email to the destination.

3. Let say we are sending email to "[email protected]", SMTP must connect to the domain "mydomain.com" on some TCP socket, and there must be some service listening on the server "mydomain.com" to receive the emails. I want to know what this service is?? On what port does it runs?? This stage is what I mean to say the "Receiving Mail Server".

POP/IMAP comes secondary after the email delivers on the server, their primary function is to fetch the email from server to the local computer.

Thanks a lot in advance!!

Answer 1

That service - which listens to receive e-mails on mydomain.com - will be the local SMTP service, which listens on TCP port 25.

You send e-mail through SMTP protocol to an SMTP server which receives your e-mail from your SMTP client. The SMTP service will deliver/store it for the appropriate mailbox, ready to be picked up - over a different protocol, POP3, IMAP - by the mail client.