Sorry you guys already might be aware of this, or its not officially supported on Ubuntu 18.04, but wanted to make a note.
I just upgraded my Ubuntu 16.04 to 18.04 and everything is working great... the only issue I found was DKIM stopped working. It worked great on 16.04 and when I use https://protodave.com/tools/dkim-key-checker/ I get DNS QUERY: default._domainkey.excolollc.com QUERY STATUS: Success
I tried to follow the rabbit and the only thing i found was that "perl" has been upgraded in 18.04 especially package " libmail-dkim-perl_0.44-1_all"
I can validate USER1: amavisd-new testkeys TESTING#1 excolollc.com: default._domainkey.excolollc.com => pass
All the settings are there from before, but DKIM is not signed.
Thank You Tom