I'm being blocked from sending group messages

Outlook.com and new Outlook enforce sending limits and spam protections that can block or throttle bulk or group messages, even for legitimate senders. When those limits are hit, messages may fail to send or be treated as potential spam.

To improve the chance that group messages send successfully:

1. Reduce the size and frequency of group sends
   • Send to fewer recipients per message than before.
   • Space out sends over time instead of sending many large groups at once.
2. Check for non-delivery reports (NDRs)
   • If any of the failed group messages generated a bounce/NDR, review it carefully. Common reasons include:
     • Invalid addresses
     • Recipient mailbox full
     • Recipient server issues
     • Message flagged as spam by the recipient’s server
   • If the NDR indicates spam-related blocking, ask recipients to add the sending address to their safe senders list. See Safe Senders in Outlook.com.
3. Make sure the account is in good standing
   • If the Outlook.com account is relatively new or recently reactivated, it may have a lower temporary sending quota until more normal usage is established. For details, see Sending limits in Outlook.com.
4. Keep messages simple
   • Avoid very large attachments (over 25 MB total) and excessive links or spam-like wording, which can trigger filters.

If group messages still cannot be sent after reducing recipient counts and spacing out sends, and no clear NDR explanation appears, contact Outlook.com support from the web interface so the account can be checked for any sending restrictions.

References:

• Can't send or receive email in Outlook.com
• I can't send or receive messages in Outlook
• Block or unblock senders in Outlook