I'm surprised to hear that. I've never had a problem with an ISP blocking SMTP.
This requires that your mail provider supports that port, of course, which is unfortunately not always the case.
They block port 25 to prevent open relays on their network (i.e. someone sends a forged email, the SMTP server does no authentication, and just forwards it on to the destination).
Plus I just like having my data here, and not somewhere where I have no physical access.