Is an email valid if it ends with a digit ? e.g.
cat@cool.thing89
With the knowledge that an email consists of [local section]@[domain section]...
An unbracketed domain consists of labels separated by periods and less than 253 characters.
Labels can be quoted or unquoted (unquoted labels must consist of
a-z, A-Z, 0-9, or any of !#$%&'*+-/=?^_{|}~or ` and have at least one character)The right-most label must be all alphabetic.
...it is not possible for an email to end in a digit, as the domain must either be bracketed (surrounded with []) or end with an all alphabetic label or one that ends with a quote. Also, here's the relevant RFC:
The top level domain must be all alphabetic. (RFC 3696, section 2)
Taken from here.