Control emails to groups

I have a problem with controlling emails to groups. I can lock down specific groups to not be available for specific people within Notes. People with Notes IDs get eg. denied/allowed to send to employees@mydomain.com.This works great and also forbids regular users on the Internet to send to this emailgroup. (Viruses, etc)

The only problem, I have is, that we have some users, who are using IMAP/POP3 with authentication on SMTP, and these people cannot send to the groups either, although they are allowed in the “Who can read this document”

Am I doing something wrong?

Thanks for your help.