When I've tried to set up my account with a mail tag, it was rejected because the mail address weren't valid according to your verifier. My mail provider uses # as character for address tags. When I've removed my address tag, I could sign up.

The # character is allowed in the local part of email addresses. Citing RFC 3696:

Without quotes, local-parts may consist of any combination of alphabetic characters, digits, or any of the special characters ! # $ % & ' * + - / = ? ^ _ ` . { | } ~

There are lots of best-practice email validators on the web, and even on SE.

marked as duplicate by Martijn Pieters, Lance Roberts, gnat, Scimonster, Doorknob Jan 28 '15 at 22:03

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  • Wait, what? A percent sign is allowed in e-mail addresses? What is the world coming to... – Mr Lister Aug 20 '14 at 9:11

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