[mobjack]

Customer complaints usually determine the spec.

If enough people wrote in about not accepting one letter email addresses, then they would likely update the validation.

But if customer service tells users to use another email address in that scenario and the customer does that, then it might not be worth the effort to fix it.

[bombcar]

It’s getting to where if you support @gmail.com and no other you’d still get 80% of signups.

Better to warm an email doesn’t look right, but let them continue if they want to

[labawi]

I think it's more likely the marketing department doesn't like people leaving fake addresses.

When I want to check postage or whatever, and they require an email address, a@b.c typically doesn't work, but [e-mail] does.