I installed the ACP Add User MOD, and in the main it's been great, but it seems that some people aren't receiving the welcome email. It's nothing to do with junk mail or any errors with the PHP mail function (if I create a user, and then force reactivation in the UCP, they get the reactivation email no problem) - it only seems to be happening with emails from the ACPAU Mod.
I've tested this with multiple email addresses / domains etc. There seems to be no consistency.
Does this Mod use the standard messenger functions of PHPBB?
Is this a known problem? Does anyone know of a workaround?
System:
- PHPBB 3.0.9
- ACP Add User MOD 1.10
- Linux / Apache / PHP 5.2.14 / MySQL 5.1.50 (hosted by Fasthosts)
Many thanks!

Martin