Outgoing Mail Restrictions let a Sponsor Administrator or Team Manager limit which external recipients a team’s mailbox can send to. Once enabled, every outbound message from that team is checked against an approved list of domains and email addresses before it goes out.
Two outbound paths share this control:
– Send Files Externally, from SharePoint Online
– Send a Message, from the File Drop Inbox
Both send from the same team mailbox, so a recipient who is not on the approved list is blocked on either path.
IMPORTANT! The Outgoing Mail Restrictions control is only available when Send Files Externally is already enabled for both the sponsor and the team. Send a Message from the File Drop Inbox has no separate enablement of its own — it becomes available whenever Send Files Externally is enabled, so one setting governs both paths.
Enable Restrictions
To enable restrictions:
1. Open Manage Teams and select the team.
2. On the Details tab, find Outgoing Mail Restrictions below Send Files Externally.
NOTE: It reads No Restrictions by default.
3. Change it to Restrict Recipients.
4. The Only Send Mail To field displays empty. Add each approved domain or email address. Typing a semicolon, a space, or pressing Enter turns the entry into a chip.
5. Select Save.
Build Allow List
The Only Send Mail To field takes a single combined list — you are not choosing between domains or addresses, you can mix both.
- A domain entry (primeco.com) approves any recipient at that domain.
- A full email address ([email protected]) approves only that one
mailbox. - Domain matching is exact and case-insensitive. Approving primeco.com does not also approve mail.primeco.com — list a subdomain separately if it needs its own approval.
- The field holds up to 1,000 characters in total.
- Restrictions cannot be saved with an empty list while Restrict Recipients is selected. To block all outbound mail for a team, disable the team’s outbound features instead of saving an empty allow list.
Turn Restrictions Off
Setting Outgoing Mail Restrictions back to No Restrictions stops enforcement but keeps the saved allow list — it is not cleared. Selecting Restrict Recipients again redisplays the same list, so you can review what you are turning back on before you save. To remove entries permanently, edit the field directly.
What happens when mail is sent?
With restrictions active, every recipient in To, CC, and BCC is checked against the allow list, on both Send Files Externally and Send a Message.
- If every recipient matches the list, the message sends normally.
- If one or more recipients do not match, the entire send is blocked. No message goes out, not even to the approved recipients. The sender stays on the form with their entry preserved, and an error names every recipient that was not approved.
Audit Trail
Enabling restrictions, changing the allow list, and turning restrictions off are all recorded in the audit log. Attempts to send mail that get blocked by this feature are not yet recorded as a separate audit entry. That is planned for a future release.