Opinionated postfix

Features

Receives email from XCLIENT-enabled STARTTLS-stripping proxy, hence no encryption needed/supported.
Forwards received email to LMTP client, hence has no access to previously received email.
Uses DKIM milter running in another VM/container.
Skips DKIM milter for mail received to port 26 - currently this makes it possible to configure your email system to sign outgoing, but not verify incoming messages.
Verifies that local user exist (listed in a text file) before doing spam check of incoming emails.
considers both + and - as "recipient delimiters", so you can use both "user+site@example.com" and "user-site@example.com" for registering on websites - they both will be delivered to "user@example.com", and you can easily track who leaked your email.
Does not perform spam-check against emails sent from addresses listed in known_senders.txt file, thus your friends' mail will never go to spam!
Does not perform spam-check against emails sent to addresses with recipient delimiter (+ or -) in them, thus those registration emails will never go to spam!
uses one RBL for spam check.

Edit "mydomain" in data/conf/main.cf file
Add data/conf/users.txt file with emails of users who are expected to receive emails via this server, using format like this:
```
  alexey@example.com ok
```
Add data/conf/known-senders.txt file with emails whose senders should not be spam-checked, using same format.
Optionally, add data/conf/aliases.txt file with email aliases like this:
```
  abuse@example.com alexey@example.com, root@example.net
```
Yes, it allows you to forward messages to other servers - be careful, though, not to become a spamer!
Optionally, add data/conf/transport_maps.txt file with emails delivery to which should go via dedicated SMTP servers.