Starting with nmh 1.7, nmh defaults to port 587 instead of 25 for SMTP
submission.
Personally I think this was a mistake. SMTP is port 25, SUBMISSION is
port 587. If something says SMTP, what comes to mind is port 25, not
587.
Sigh. I understand why you would say that, but think about nmh's role.
587 is the port that is supposed to be used by MUAs to submit mail.
nmh is a MUA; it seems perfectly logical to me that the default that
is used by nmh is the submission port. Yes, the PROTOCOL that is being
spoken over port 587 is SMTP, but that doesn't seem relevant to the
appropriate default.
Also, super-common to have ISPs blocking outgoing port 25 to prevent
compromised PCs from acting as spam generators; port 587 is your only
option here.
--Ken