I run an email server with ten domains on it. Hotmail blocked me once, but I had no problem getting that lifted. No other issues for over five years now.

I have more of a problem with mail going the other way. I use a number of online spam traps to avoid spam, and my gf's Yahoo account often gets bounced by them.

Specific Yahoo servers regularly get flagged for spam, and if you're using a Yahoo account your mail will be filtered by many, many servers if it's sent from one of those IPs.