Strip non-numerical characters from the "email address"

I'm doing a write-up to submit to the higher-ups to see if we can implement ClickSend into our workflow, but our software where we enter email addresses appears to have limited support for emails starting with a # (one field won't accept it, one will but it's unclear if it will work).

If we could enter a phone # email as, e.g. z5555555555@sms.clicksend.com, and any letters (z in this case) would be stripped out by your software, then it could work.