There is a growing trend to use port 587 for all client to MTA communications. It's in a standards track RFC: http://www.ietf.org/rfc/rfc2476.txt
My question is "Why?". Why have 2 instances of a SMTP server running on the same server, if they both do the same thing? What security feature does it provide, besides giving me 2 things to troubleshoot as an administrator.
This just seems like unnecessary complication that isn't needed unless the ISP blocks port 25. Even then, if the ISP is blocking port 25 to prevent spam, it just means it will just take a little more time until port 587 is blocked too, and we will have to use a different port altogether.
Just seems like we are creating more work for ourselves rather then solving the problem and authenticating SMTP to begin with