Suppress out-of-office replies for messages delivered to groups

[p-try]

Currently, when an email is sent to a distribution group (e.g., sales@company.de), recipients receive out-of-office (OOF) auto-replies from each individual group member who is away. This behavior can be confusing and noisy for senders, especially when multiple members are on vacation.

As noted in the Grommunio community forum , this differs from the behavior of Microsoft Exchange, which suppresses OOF responses when a message is sent to a group address.

This issue specifically concerns server-managed distribution groups (not client-side mailing lists). The existing OOF suppression logic does not currently account for messages addressed to such groups, leading to unwanted auto-replies.

Expected Behavior:
Out-of-office replies should be suppressed when the original message is sent to a distribution group address.

Proposed Solution:
Implement logic to detect if the recipient is a distribution group and suppress OOF auto-replies accordingly during message delivery.

This enhancement improves user experience and aligns Gromox/Grommunio behavior more closely with established enterprise email standards.