I've run Linux on all my machines for 18 years, but have never needed to understand the workings of email, as I've always used shared hosting and cPanel. Now I'm setting up my own server and I'd like to understand the actual mechanics of email.
I've read several Postfix docs including http://www.postfix.org/OVERVIEW.html and still don't get it. It seems that Postfix is only an SMTP server; it only listens on 25. If I understand, it listens on 25 for incoming mail, processes it, then saves it in a flat file. - If someone sends me an email to char...@example1.com, example1.com resolves to some IP which finds my Postfix server on 25. That email is then stored at /var/spool/mail/charles right? - What if I want to receive email in the name of someone who does not have a passwd account on that machine? How does that work and how would I set it up? - If someone then sends an email to me at charles@example*2*.com, how can I differentiate that email from the one to example1.com? - So these emails are now stored on my mail server. How do I get them to my workstation, and where would they go? Or would my mail client in my workstation fetch them directly from the mail server, and if so how? - If this is how things work, what role does pop3 or imap play? I've always used Thunderbird as a mail client, and I've always set it to fetch from mail.example1.com. How would my workstation and the DNS system know where mail.example1.com is? There's nowhere to set it in Postfix, and there doesn't seem to be a virtual hosts function. - I have never been able to make Thunderbird fetch local mail from /var/spool/mail. Is there some trick, or a better way? I'm not wedded to Thunderbird but it does store email where I want it and in a flat-file, unlike a number of other clients, and it is easy to use.
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