Hi Tom,
möglicherweise gibt es in Deinem Directory Gruppendokumente bei denen in den Properties (unter dem Security Tab), Reader gepflegt sind. Sobald nun ein User, der nicht in dem Feld steht, versucht eine Mail an diese Gruppe zu schreiben, erscheint diese Fehlermeldung.
Schau mal nach ob das so ist. Siehe dazu auch diesen Auszug aus der Adminhilfe (den Du zur Lösung Deines Problems umkehren müsstest) :-)
By default, all users can send mail to groups defined in the Domino Directory. To reduce unnecessary mail traffic, you can edit the reader fields for a Group document to restrict access to the group, specifying the users who are allowed to send mail to the group. Only users to whom you grant reader access can send mail addressed to the group. Users who do not have access to the group can see the group name listed in the Domino Directory and choose the name in the Select Addresses dialog box, but the Router rejects the message if they attempt to send a message to the group.
The restrictions apply to messages sent to either a group's Notes address or its Internet address and to messages originating from a Notes client as well as messages sent and received over SMTP (as from an IMAP or Notes client). From a Notes client, a user who does not have permission to use the group receives an error when attempting to send mail to the restricted group. If the same user attempts to mail from a POP3 or IMAP client, the Router generates a Nondelivery reports indicating that the sender is not authorized to send mail to the specified recipient.
To restrict users from sending mail to a group
1. From the Domino Administrator, click the People & Groups tab, expand the Domino Directory that contains the group you want to restrict access to, and select the Groups view.
2. Right-click the Group document to manage and choose Document Properties.
3. Select the Security tab (the Key).
4. Deselect the All readers and above checkbox to enable editing of the readers list.
5. To enable a user to send mail to the group, select the user's name in the list.
6. To provide access to users not listed, click the Person icon to the right, add the name in the Select Names dialog box, and click OK. The user's name appears at the bottom of the list with a check next to it.
7. Deselect the names of users you want to prevent from sending mail to the group, including the Anonymous entry.
8. Close the Document Properties dialog box.
Gruß
Daniel