My chosen email address, which has worked for years at other Stack Exchange sites, was today rejected for a question at Physics Stack Exchange, and again here at the corresponding Meta.
In this case, the email address is
RFC 3696 makes it plain that any printable character is valid in an email address, given the protocol rules. So, for example an email address containing a punctuation character (
~, etc.) in the local part is valid so long as it follows the standard.
Indeed, in the local-part (the part before the final
@ character), any character may appear in a valid email address. It's not up to the sender to decide what is and isn't a valid local-part.
Hence, they should not be rejected in filtering routines but, should instead be passed to the email system for evaluation by the destination host.
Please ensure the Stack Exchange software does not reject valid email addresses chosen by the user for their notification address.