Sending emails with postfix via port 587 on gmail

Question

Since my ISP blocks port 25 I'd like to be able to configure postfix to send smtp email over port 587. Every time I try to send an email I see this in the mail.log

Oct 17 10:37:49 new-host-2 postfix/smtp[1552]: connect to aspmx.l.google.com[74.125.113.27]:25: Operation timed out

I'm assuming this is due to the fact that this doesn't work over port 25. What do I need to modify in order to get smtp to communicate over port 587? I tried using port forwarding but that wasn't working either.

Not sure but I think if I can get the mail.log to show [74.125.113.27]:587 this would work. Any idea how to switch this?

Thanks in advance!