when you open smtp settings in script step "send email via smtp", it shows port 25, not important what it was programmed before. if you open and save the script, port saved as 25.
interesting thing, if you change port to another number and save the script, it correctly remembers the port you set. but you won't see it in FM15/FM14 Windows client. but if you open the script in FM12, or in OSX, you see that the port was successfully changed.
again, this effect appears only in Windows, in OSX there is no this bug.
the workaround is simple - just don't open smtp settings in windows.
but strange that this bug is lasting from at least v.14