ISEMAIL_RFC5321_TLDNUMERIC

[tredoe]

Also, the type of diagnosis "ISEMAIL_RFC5321_TLDNUMERIC" should not exist because the definition of address literal includes brackets in both RFCs 5322 and 5321.

[dominicsayers]

This is intended to diagnose the situation where a user enters an address literal without the brackets.

Such an address has a valid domain name format but extremely unlikely to be a real domain name. This allows us to warn the user that the email address is suspicious without saying it is de facto an invalid address.

I think it is a useful diagnosis.