How to match a comma separated list of emails with regex?

Question

Trying to validate a comma-separated email list in the textbox with asp:RegularExpressionValidator, see below:

Answer 1

^([\w+.%-]+@[\w.-]+\.[A-Za-z]{2,})( *,+ *(?1))*( *,* *)$

The point about requiring a comma between groups, but not necessarily at the end is handled here - I'm mostly adding this as it includes a nice subgroup with the (?1) so you only define the actual email address regex once, and then can muck about with delimiters.

Email address ref here: https://www.regular-expressions.info/email.html