Another interesting part of dots in emails is that they apparently can't be at the end of the username, EXCEPT if you also "quote" the entire username. So, <a.b

Another interesting part of dots in emails is that they apparently can't be at the end of the username, EXCEPT if you also "quote" the entire username. So, <a.b.@example.com> is probably invalid but <"a.b."@example.com> (including the "quotes") is supposedly valid. Had an acquaintance who was signed up to a popular email service with "a.b." (their initials) for years until they changed their underlying platform, after which they actually were very sorry to let him know that they could not support his strange email address any more and terminated the account.