Can no longer email my whole contact group

Hi @Erin McClymont

Thank you for posting your question in Microsoft Q&A. 

I understand that your business account is currently experiencing issues when sending marketing emails to a large group of members. 

Based on your description, this behavior is quite common when using a standard Outlook/Exchange Online setup for bulk or multi‑recipient emails. Microsoft applies strict anti‑spam and rate‑limiting policies, and high‑volume sending can trigger throttling, temporary blocks, or message rejection. 

You can refer via: Exchange Online limits - Service Descriptions | Microsoft Learn 

You could try to follow these steps to troubleshoot it: 

Wait before attempting to send again 

If you recently hit a sending limit or were throttled, Outlook may temporarily restrict your account.  Please wait 24–48 hours before attempting to send another batch of emails.  This cooldown period often resolves temporary throttling or rate‑limit blocks automatically. 

Split the email sends 

Break your recipient list into smaller batches (for example, 200–400 recipients per batch) and send them over intervals or on different days. Allow sometime between each batch to avoid the 30‑messages‑per‑minute throttling limit. 

Check for sending restrictions 

Please ask your administrator to verify whether your mailbox appears in the Restricted Entities list in the Microsoft Defender portal.

If your mailbox has been restricted due to suspicious activity or potential spam, your admin may be able to remove the restriction directly from that page.

References: Remove blocked users from the Restricted entities page - Microsoft Defender for Office 365 | Micros… 

Improve email-sending practices to reduce spam flags

Use clear, non‑promotional subject lines, include an easy opt‑out option, personalize content when possible, avoid excessive images or hyperlinks, and ensure your domain has proper SPF, DKIM, and DMARC configurations in your tenant.

To better address your issue, could you provide additional information for the following question:

How many recipients are included in each send, and how frequently does your account send emails to your members?

Have you received any NDR (Non‑Delivery Report) or bounce‑back messages?

Please understand that our initial reply may not always immediately resolve the issue. However, with your help and more detailed information, we can work together to find a solution. 

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