I just set up a wildcard email forwarder on my domain and set up an email address for every domain or website I sign up for (e.g. [email protected]). Keeps everything nicely separated, logins are predictable, and I can track who got my email from where.

It makes certain things more complicated, like authenticating against certain services, or if someone sends and invitation to one of your domain emails, but it works just fine 95% of the time.