Mail Server: Dovecot & Anti-Spam

In OpenDKIM, what is the division of labor between signing.table and key.table?

Postfix is running and can already send and receive mail on the server itself, so why do you still need Dovecot for external clients like Thunderbird or a phone?

A client can reach IMAP on port 143 with no encryption at all, yet port 993 refuses any unencrypted connection — what accounts for that difference?

Dovecot's config files run to 1,500-1,800 lines yet almost none of them do anything — how do you see just the settings that actually deviate from the defaults?

Dovecot auto-detects mailboxes and it worked in testing, so why is it still recommended to set mail_location explicitly in 10-mail.conf?

A macOS Mail user keeps hitting 'Maximum number of connections from user and IP exceeded' against your Dovecot server — what limit is being tripped and how do you raise it?

When you set up a mail account against a plain Dovecot server, where do the username and password actually come from?

Postfix supports SASL yet you still have to bring Dovecot into the picture to let remote users send mail — what does Dovecot actually contribute?

In the Postfix main.cf SASL block, smtpd_sasl_path is set to 'private/auth' rather than the full /var/spool/postfix/private/auth — why the relative path?

A mail client's setup screen warns it will send a 'Normal Password' / plain-text password — with STARTTLS enabled, is that actually a security problem?

How does SpamAssassin actually reach a spam verdict, and what does it stamp on the message so clients can filter it?

Legitimate mail is landing in the spam folder because SpamAssassin scores it too aggressively — which local.cf setting do you adjust, and in which direction?

How is SpamAssassin wired into Postfix's delivery path so that incoming mail actually gets scanned?

You want to prove your spam filter is live without waiting for real spam to arrive — what standard test message forces a spam verdict?

SpamAssassin already tags spam with headers, so why does moving that spam into a server-side Junk folder need two extra pieces of software?

To send incoming mail through Dovecot's LMTP so Sieve can file spam, which Postfix main.cf setting hands delivery over?

What role does ClamAV play on a mail server, and what does freshclam do for it?

You deploy ClamAV on a small 1 GiB cloud VM and the daemon keeps dying on its own — what is happening and what is the practical floor for RAM?

How do you confirm ClamAV is scanning mail without exposing your server to a real virus?

SPF, DKIM, and DMARC all live in DNS TXT records — how do their jobs actually differ?

An SPF record ends with a qualifier for 'everything else' — why is the softer ~all usually recommended over the strict -all?

What exactly does DKIM let a receiving mail server prove that SPF cannot?

OpenDKIM runs as a milter in 'Mode sv' — what do those two letters switch on?

What does opendkim-genkey produce, and which options control the key size and its name?

opendkim-testkey reports 'key not secure' on your new DKIM key — is that a problem you need to fix?

Wiring OpenDKIM into Postfix, why is milter_default_action set to accept, and where do you point the milter parameters?

Postfix has both smtpd_milters and non_smtpd_milters — which mail does each one filter?

You're enabling DMARC for the first time — which policy value should you start with, and why not jump straight to reject?

Beyond setting a policy, what practical intelligence do you get by adding a rua address to your DMARC record?

Why bother implementing SPF and DKIM at all if spammers can adopt them too?

You read some mail in Mutt and on quitting it offers to move read messages to ~/mbox — why can answering yes lock you out of that mail from other programs?

In Mutt, mail composed as peter goes out as peter@host1.a-company.com, but you want just the domain a-company.com as the sender — how do you fix the hostname, and why does it depend on the distro?

For a user who checks the same account from a laptop, phone, and tablet, why is IMAP the right retrieval protocol and POP the wrong one?

You install Dovecot on Ubuntu the same way that worked on RHEL, but IMAP still isn't available — what's different about how the two distros package it?

No internet standard requires a reverse DNS entry, yet mail from your new server keeps getting flagged as spam — how does reverse DNS factor in, and where is it configured?

What is the single worst configuration mistake you can make on a mail server, and why is it so hard to recover from?

Dovecot refuses to start after you condensed an empty block to protocol imap { } on a single line — what syntax rule did you break?

In Dovecot's 10-ssl.conf the cert line reads ssl_cert = </etc/dovecot/private/dovecot.pem — what does that leading < do, and where are the default certs per distro?

Setting mail_location for mbox storage in /var/mail, why must the Mail directory come before INBOX, and why keep it even when it holds no mail?

After enabling SMTP auth through Dovecot, some mail clients still can't log in — which single value in 10-auth.conf is usually missing?

In SpamAssassin's local.cf, what does report_safe control, and how do its values 0, 1, and 2 differ?

Wiring Dovecot LMTP for spam-to-Junk delivery, why do you set auth_username_format = %Ln in 10-auth.conf?

The spam-to-Junk procedure installs dovecot-managesieved on Debian/Ubuntu — what's the RHEL equivalent, since that package doesn't exist there?

Once ClamAV is filtering mail through Postfix, how can you tell it scanned a message, and what happens to the sender when a virus is caught?

You open the header of a mail signed by OpenDKIM and see a DKIM-Signature line full of one-letter tags — what do a=, d=, s=, bh=, and b= mean?

Dovecot is running and configured, yet external clients on a Fedora/RHEL/SUSE box still can't reach IMAP or POP at all — what stops them before Dovecot ever sees the connection?

Yahoo runs DMARC strictly with a reject policy — why does that specifically break mail sent through mailing lists?

You send a one-word 'test' mail to mail-tester.com to check your server and it fails the spam test — what did you do wrong?