The biggest problem I've had over the years is getting an ISP to give me IP addresses from a good static block. If there are dynamic addresses within that block or lots of spam coming from IP addresses from your provider then you're toast. Currently have a customer I have set up email servers using AT&T uverse business DSL with static IP addresses. No problems. I'm running qmail with starttls . I used mxtoolbox to check my server and implemented all recommendations. So far I've had no problems. The customer maintains cell sites for all the major cell companies - Verizon, Tmobile, Sprint, AT&T, etc and uses the server mainly to communicate with them with no problems.