Mail server not working after upgrade

Question

After a few hours, my server finally came back up however mail is not working.
In the /var/log/mail.log I see many error  messages related to the same thing from Postfix whenever an inbound mail is recieved.
May 24 06:26:22 my.server.com postfix/postscreen[25712]: CONNECT from [62.13.138.73]:64283 to [192.168.0.3]:25
May 24 06:26:22 my.server.com postfix/postscreen[25712]: fatal: error seeking /Library/Server/Mail/Data/mta/postscreen_cache.db: Invalid argument
May 24 06:26:23 my.server.com postfix/master[54]: warning: process /usr/libexec/postfix/postscreen pid 25712 exit status 1
Help!

Answer 1

I'd guess that the postscreen database is missing or corrupt.
please issue the following Terminal.app commands:
postconf -n -c /Library/Server/Mail/Config/postfix/ | grep -i postscreen
postconf -c /Library/Server/Mail/Config/postfix/ | grep -i postscreen
and anonymize the output if and as desired.   If you anonymize, please consistenty replace the domain portion of your URL(s) to example.com, example.net and/or example.org (these are RFC-reserved bogus domains) and replace the server's host name to something else if that's more sensitive than "mail" or "www" or "server" — consistency in these changes is important — and alter any IP addresses included (other than 127.0.0.1 / localhost) to 10.20.30.40 (or some other private IP address — again, consistency in these changes is important — and then post that output here.
Before making any changes, get a complete system backup or two, on an external disk.  That's your path back if something here goes badly wrong, weird or otherwise untoward.
Once there are complete backups and entirely as a test / guess / experiment, I'd look to rename an existing postscreen database out of the way and see if a new cache database gets created, and would also check the file ownerships and protections of the files in that area.
$ sudo ls -ale@ /Library/Server/Mail/Data/mta/
Password:
total 48
drwxr-x---   5 _postfix  mail     170 Jan 30 15:20 .
drwxr-xr-x  13 root      wheel    442 Jan 28 10:57 ..
-rw-------   1 _postfix  mail      33 May  5 16:08 master.lock
-rw-------   1 _postfix  mail   16384 May 24 08:22 postscreen_cache.db
-rw-------   1 _postfix  mail    1024 May 24 10:04 prng_exch
$
The two files that are most interesting in the above are the . and postscreen_cache.db files.
There is also an upgrade log around, and you'll definitely want to have a look in that — to see what (else?) went wrong here.  (Off the top, I don't recall the name of the upgrade log file.  In recent releases, it's usually something like /var/log/install.log — also check the system logs for "upgrade" messages.)