In CB User Management I want to add a user with email that begins x'sabcd@xyz.com. (That is an apostrophe.) When email is sent to this address with Thunderbird, it is accepted and delivered. So the address is valid in some uses.
After entering this, CB responds that the email "seems valid".

But upon 'saving' the checker (Ajax) (or something) reports that "this address does not accept email".

I have spent a bunch of time searching com_profiler .php code for a place where acceptable characters are defined but I have not found it.

In any case, CB is configured Ajax name check = NO and Ajax email check = NO.

I have searched for "email syntax" in this forum and failed to find my problem discussed.

All help much appreciated.
---M

Thanks for your reply. I know the address does not conform to standard email address syntax. Nevertheless, like the bumblebee, it flies (receives mail):

By test just run: "Your message was successfully delivered to the destination(s)listed below. ...
The mail system
<d'smail@xxxx.xxx>: delivery via
smtp.xxxx.xxxx.com[208.47.xxx.x]:25: 250 OK D1/DE-10482-4A54F4C4"

Rock: finding the regex code
hard place: asking d to change email address
I'll just see if d has another one.