Not all ISP's are going to be that draconian. My guess is that the ISP's (especially the ISP's serving some highly-trafficed WiFi networks) with experience of spammers using their network for an email blast are the ones who learned to put in an access list that prevents port 25 from being forwarded on their outbound links. Other ISP's that have better control of who gets on their network probably have not had the pleasure of a spammer using their network to originate outbound spam.

The access list I'm talking about would be configured on a cisco or other router that is the BGP peering point for the ISP. Most of your user-supporting techs won't ever see the ACL's that go onto those routers.