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Hi,

As you may know I am working on a home PHP webserver.

I have the LAMP stack operational along with BIND and Let's Encrypt.  I 
need to understand and get Postfix and Dovecot functioning.

Here is what I have pulled together.  Please le me know if this is 
accurate, if I let anything out, or any other information I need to 
know.  Thanks!!

MUA  : Mail User Agent – Your email client.  (port 587)

MTA  :  Mail Transfer Agent (port 25) (port 587 or 465 ?)

MDA  : Message Delivery Agent

MSA  : Mail Submission Agent

SMTP  :  Simple Mail Transfer Protocol

POP3  :  Post Office Protocol

IMAP  :  Internet Message Access Protocol

SSL  :  Secure Socket Layer

TLS  :  Transport Layer Security

• User client (Mail User Agent) sends an email to the Mail Transfer 
Agent via port 25, 587, 465, or 2525.  I’ve read that port 465 should no 
longer be used.
• I read port 587 should only be used for submissions (i.e., mail client 
to mail server), port 25 should only be used for relaying (i.e., mail 
server to mail server communications).
• Mail Transfer Agents transfer email to other Mail Transfer Agents via 
port 25 exclusively.
• Mail Transfer Agent stores the email on the server.
• The user client (Mail User Agent) interacts with the mail server via 
the Message Delivery Agent using POP3 or IMAP.  This transaction can be 
secured by a Secured Socket Layer certificate referred to as TLS 
(Transport Layer Security), POP3S or IMAPS, or not secured POP3 or IMAP.
• The POP3 and IMAP and ports:
         ◦ IMAP - 143
         ◦ IMAPS - 993
         ◦ POP3 - 110
         ◦ POP3S – 995

Thanks!!