We also think a separate log for submission (587) port and "between servers" port 25 would have been very useful.
We also don't want user to be able to authenticate on port 25 and have them only use port 587. Also it seems port 25 allows authentication without starting a TLS session first which is really bad.
On our side, and as we are using an incoming SMTP filtering gateway (e.f.a), our workaround for this was to redirect all port 25 traffic originally directed to our SmarterMail to our SMTP incoming gateway.
So port 25 of SmarterMail is never reached from outside, but only from our filtering gateway for forwarding traffic to SmarterMail after spam analysis.
Then our logs for port 25 is on the mail filtering gateway and for 587 in SmarterMail's SMTP log.