Linux · Mail Server: Postfix

Your mail sends fine but recipients keep flagging it as spam. Reverse DNS is mentioned as a defense — what does a PTR entry do and how does its absence hurt you?

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More in Mail Server: Postfix

A colleague says the mail transfer agent is the whole email server and drops mail into users' inboxes. Where is that wrong, and what actually does the local delivery?

In mail-server terminology, what do MUA, MDA, MTA, and SASL each stand for, and which one is the client program the user actually sees?

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When storing incoming mail, what is the practical difference between mbox and maildir format, and which one is recommended alongside an IMAP server?

You add an entry to /etc/aliases to redirect root's local mail to your own account, but nothing changes. What step was missed?