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problems checking large quantity of backup mails via Office365




We check our customer backups by monitoring a mailbox that receives mails from their backup software. But a while ago PRTG started throwing errors saying "Could not access the mailbox (PE: 124)".

We are thinking this is because of some limits set on Exchange Online. A Microsoft Engineer confirmed this to us. But now we need a solution for this problem.

We are currently doing 100 checks.

We tried spreading the checks by setting it to scan every 4 hours and creating schedules as following: schedule1 - Pause from Saturday 9:00 until Tuesday 9:00 schedule2 - Pause from Saturday 9:10 until Tuesday 9:10 schedule3 - Pause from Saturday 9:20 until Tuesday 9:20

There is one schedule for every 10 mails.

This does not seem to help though. Most checks started failing again.

Anyone that knows how to fix this?

I also should say that these checks sometime take around 400 seconds to complete. Which is way longer than it should.

backup backup-monitoring imap office-365 office365

Created on Mar 23, 2016 9:06:23 AM

4 Replies



are those emails all are received in the same inbox?
Best regards

Created on Mar 24, 2016 2:52:16 PM by  Konstantin Wolff [Paessler Support]



Hi, I have the same error Could not access the mailbox (PE: 124) when using IMAP to monitor a Office 365 mailbox which is dedicated to receiving backup notification emails. I'm trialling the software with a view to purchasing if I can get this working correctly. I have set up 46 sensors to look for client backup emails and have many more to add - all of the emails are being delivered into the same inbox. How can I resolve this please?

Created on May 5, 2016 1:42:27 PM




The sensors need their time to perform there scan, and it's likely that the target mail-server limits parallel connections toward the inbox. Can you check if there is such a limit, and how high it is?

Created on May 6, 2016 12:01:45 PM by  [email protected]




I created a case on Office365 sometime ago for this issue.

I think the engineer has let me known that only a maximum of 10 or 20 concurrent connections to a single mailbox are allowed. So this is an Office365 limitation.

You should be able to solve this by running the checks in smaller batches. You can do this by creating schedules and applying them to the sensors.

Created on May 6, 2016 12:06:40 PM

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