I was upgrading vom version 2.0.9 to 2.2.3a and the mail verification is not runing any more since then.
When new members want to subscribe I'll get the following error:
You are now registered. However, we were unable to send the activation mail to your email account due to an internal error that had occurred on our server. We are sorry for the inconvenience, please send the webmaster an email notifying him/her of the situation.

All other mailfunctions are running.
Can you please help me to fix that problem?