I'm a Mac user, but I don't think this is a Mac-only question.
I have successfully switched my outgoing mail from using port 25. I switched to port 465 using SSL. Comcast's help directs users to use port 587.
Since port 587 doesn't seem to support SSL, is there a reason why I should use it over port 465?
I created a page showing the screens users see in Mac OS X 10.5 using Mail.app to make this change since many of us set up our accounts using port 25 so many years ago. You can see it at my Mac Mail Setup page. The Comcast help on this matter is for Mac OS X 10.4 and says to use port 587.
I'm with Cajun, 465 with SSL. The problem with 587 is that it used to not allow access from outside of Comcast, whereas 465 with SSL and authentication does. I haven't checked it recently, but Comcast's own FAQ about access to the mail servers from outside of Comcast says use 465 with SSL, so that's what I do.
Oh, and 587 does work with SSL last time I tried it.
587 and 465 are designed to work while roaming off the Comcast network. You can use SSL on either and both require authentication. The only real difference between the two is 587 is optional on SSL but it's mandatory on 465.