This week I experienced that the contribs smeserver-fetchmail (retrieve mail from pop3 accounts) and dungog-mailblocking (restrict mails to a user to certain domains) do not work together. If installed both , mails fetched from a pop3 account are rejected. As I was very eager to use both the contribs I did some debugging and testing.
I found out that a mail fetched by fetchmail is offered to the local smtp server and addressed to accountname@mail.yourdomain.com . The mail rules created by dungog-mailblocking do not permit mail addressed to accountname@mail.yourdomain.com, but do permit mails addressed to accountname@yourdomain.com i.e. without 'mail.' prefixed to the domain.
The solution for this is very simple: just create for each account that has fetchmail enabled an accept rule on the 'E-mail blocking' page. Accept from *@* to accountname@mail.domain.com and you're done!
All rpm's involved:
dungog-mailblocking-1.0-4.noarch.rpm
perl-CGI-FormMagick-0.89-08.noarch.rpm
smeserver-fetchmail-1.3.4-02.noarch.rpm