Feature request:

1. Please allow the blocking of domains and IP's by means of a list.
2. Please allow additional blacklists, graylisting
3. Please allow additional signatures for Clamav. (I am still getting zipped virusses through)
4. Please allow for better security (only allow an account to send if the address exists in the alias list)

1: Create a recipient hash:
smtpd_recipient_restrictions =
...
check_client_access hash:/etc/postfix/blacklist
in /etc/postfix/blacklist :
1.2.3.4 REJECT
domain.ltd REJECT
3.2.1.4 REJECT

Also possible in spamassassin:
vi /etc/mail/spamassassin/local.cf
blacklist_from [email protected]

2. https://wiki.apache.org/spamassassin/DnsBlocklists

3. There are many projects out there. One of which: https://github.com/extremeshok/clamav-unofficial-sigs

4. smtpd_sender_restrictions = 
    permit_mynetworks
    ... 
    check_sender_access hash:/etc/postfix/sender_access
    reject_unknown_sender_domain
    warn_if_reject reject_unverified_sender 
   

http://www.postfix.org/ADDRESS_VERIFICATION_README.html

I know how to configure mail servers. But I'm stil _very_uncomfortable around docker.
As we speak I run 2 docker-mailserver instances, One in production, another in test.
Once I got everything set-up in a stable manner, I'll start working on the above issues and create pull requests. Don't let this stop you from cutting in and doing something already. I'm also rather unfamiliar with git.