Comment Don't think custom domains were his problem (Score 4, Insightful) 448
Avoid custom domains for your login email address
Honestly, I don't think that would have helped. I doubt it's much harder to gain control of someone's gmail, yahoo or hotmail account if they are as motivated as it sounds like his attacker was.
Once you gain control of anyone's email account, even if the attacker doesn't have custom domains to hold for ransom, they could easily threaten bank accounts, etc etc.