I'm facing a strange situation where an automated job is sending emails from a specific mailbox, but some recipients are reporting that those messages aren't delivered. On my end, the emails appear as 'sent' in both the explorer view and the message trace, yet multiple external companies have flagged this issue.
It seems like this might be related to the high volume of messages being sent from this mailbox. For instance, there were over 2500 messages processed on one particular day when the job ran, and they were all sent within a short time frame. I'm not seeing any error messages that would indicate a limit being exceeded, though.
The recipient limit for this mailbox is set to 500, but I'm unsure if there are other limits in place, like those for messages sent per minute or hour. Has anyone encountered similar issues and found a solution?
Just to add, the problematic messages are generated by Dynamics 365 batch jobs and sent from a dedicated mailbox.
3 Answers
Don't forget to look at the specific plan you're on with Exchange Online. Each plan has different limits for sending emails, and knowing your limits can really help track down these issues. Has anyone from your IT team looked into it yet?
You could be bumping into volume restrictions with Exchange Online, especially since you mentioned sending a large number of emails in one go. Depending on your plan, there are specific limits to how many messages you can send daily. I remember reading that 2,500 emails in a day could trigger some restrictions. Check out Microsoft's documentation on this; it might help clarify if you're exceeding any limits.
It sounds like the recipients might need to check their email server's logs for more information. If your logs show the emails were handed off correctly, then the issue may lie with their provider. Also, make sure your SPF, DKIM, and DMARC settings are configured properly; these can sometimes lead to delivery issues if set up incorrectly.
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