Hi Michael,
Recipient limit-500 recipients. This is the maximum number of recipients allowed in the
To:, Cc:, and Bcc: fields for a single email message. There is no specific limit for Bcc fields.
For your reference:
Exchange Online Limits
The issue might be related to Outlook profile or a specific client side. Please try the below troubleshooting steps:
1. Try to check this issue via using
Outlook Web App to see whether the problem still occurs.
2. If user using Outlook client such as Outlook 2016/2013 then create a new Outlook profile to troubleshoot this issue. Here is the article for your reference:
https://support.microsoft.com/en-in/kb/829918
Note: If user have local data that is not present on the Cloud/Server. In that case, we recommend that you
Export the data to an Outlook Data File (.pst) before creating a new Outlook profile.
Moreover, you may also try to troubleshoot this affect user issue via using different PC (e.g. any non-problematic colleague’s PC) to determine whether it is a specific client side issue.
Best regards,
Shyamal
