[pstch]

I have even seen emails rejected when using a simple dash, or because it was not hosted by a well-known mail service provider, and even because "your email should be of the form <name>.<surname>@<website>" (yes, with a dot, ironically).

At that point I gave up, and I use a single Gmail account for all the services that I don't use very frequently (also because it's not always easy to send mail from self-hosted mailservers, some destinations simply refuse any mail that is not from Gmail/Yahoo/Hotmail).