While port 587 is the official standard port for email submission, it
doesn't *require* the usage of SSL. GMail does however have this
requirement.
Also, I'd still personally prefer to use port 465 over port 587 for mail
submission when both are available, purely because when using port 465
you negotitate SSL immediately, whilst with port 587 there is some plain
text negotiation first which *could* accidently leak identifying
information such as your hostname in the EHLO, to the Exit node.
Now, if we keep 25 blocked, are we risking undoing the benefit from that
blockage by unblocking 587? It turns out that I was rejecting exits for
port 465 and 587, so now I'm wondering whether it might be a Bad Thing to
accept exits to 587. Also, the new allocation of 465 is for urd (URL
Rendezvous Directory for SSM). Offhand, I don't know what SSM may be nor
whether accepting exits for this service would be okay.