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I've never heard of an item limit. &nbsp;I know there's a capacity limit (in terms of MB of storage) which can be set on the server.&nbsp;&nbsp;
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king daddy

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There are some limits that can affect performance :<br><br><ul><li>100,000 items per folder</li><li>5,000 items per Calendar folder</li><li>500 folders total</li></ul><br>And yes, server wise it is normally space that gets most caught out....<br><br>Have a read of :&nbsp;<a href="https://support.microsoft.com/en-au/help/2768656/outlook-performance-issues-when-there-are-too-many-items-or-folders-in" rel="ugc">https://support.microsoft.com/en-au/help/2768656/outlook-performance-issues-when-there-are-too-many-items-or-folders-in</a>&nbsp;
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Thanks Paul and Karen.<br><br>After further investigation on my part, the logs show:<br><br>Time: 5/11/2020 11:47:10 AM<br>&nbsp;Windows Event Time: 5/11/2020 11:44:00 AM<br>&nbsp;Windows Event Log: Application<br>&nbsp;Windows Event Source: MSExchangeIS<br>&nbsp;Windows Event ID: 9646<br>&nbsp;Windows Event Severity: Error<br>&nbsp;Windows Event Message: Mapi session /o=XXXX/ou=Exchange Administrative Group (FYDIBOHF23SPDLT)/cn=Recipients/cn=b5033fe51b0844e9a8e24baf63ec7453-USER NAME with client type AirSync exceeded the maximum of 1280 objects of type Message.<br><br>As such, going by the email from tier 1, I thought the user had some quota on the number of messages allowed in the inbox as the tech stated "We have received an alert that the Client / User has a full inbox of 1280 messages. As a result, they are unable to receive any new messages as <strong>Exchange has limited the inbox size to 1280 messages</strong>". <br><br>Anyway, further research shows issues with airsync that are beyond the scope of this question. I have instructed the tech to lower the limit to 2500 and troubleshoot the airsync issue. <br><br>Thanks again.
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Apologies, just noticed you had the same link in your question.... Note to self = Read the question fully.
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Thanks, Mark. That link is where I found the info about 100,000 possibly causing performance issues. Looks like an airsync issue now that I have looked into it myself.
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You can try disabling caching of shared mailboxes in Outlook &nbsp;(client side).<br><br>Anyway, I will leave it to the real Experts in this TA :)
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Greetings,<br />
<br />
A user reached a limit of 1200 messages in his inbox and is unable to receive email. The previous admin set a limit of 1200 messages. Not sure why. A tech reached out to me and said he changed the &quot;MaxObjsPerMapiSession&quot; limit to 50,000. He was instructed to increase the number a messages allowed in the users inbox. I believe the wrong reg entry was changed. I believe this limit is an Outlook limit not Exchange. There is an MS article stating that the inbox can have up 100,000 messages before one may experience performance issues, but, again, it specifically mentions Outlook not Exchange. <br />
<br />
<a href="https://support.microsoft.com/en-us/help/2768656/outlook-performance-issues-when-there-are-too-many-items-or-folders-in" rel="ugc">https://support.microsoft.com/en-us/help/2768656/outlook-performance-issues-when-there-are-too-many-items-or-folders-in</a>&nbsp;<br />
<br />
Where would one increase the number of messages allowed in an inbox when on Exchange 2016 and Outlook 2013? Is there a limit or quote on a database level for number of messages in an inbox on Exchange? <br />
<br />
Thanks for any assistance.
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Greetings,

A user reached a limit of 1200 messages in his inbox and is unable to receive email. The previous admin set a limit of 1200 messages. Not sure why. A tech reached out to me and said he changed the "MaxObjsPerMapiSession" limit to 50,000. He was instructed to increase the number a messages allowed in the users inbox. I believe the wrong reg entry was changed. I believe this limit is an Outlook limit not Exchange. There is an MS article stating that the inbox can have up 100,000 messages before one may experience performance issues, but, again, it specifically mentions Outlook not Exchange. 

https://support.microsoft.com/en-us/help/2768656/outlook-performance-issues-when-there-are-too-many-items-or-folders-in 

Where would one increase the number of messages allowed in an inbox when on Exchange 2016 and Outlook 2013? Is there a limit or quote on a database level for number of messages in an inbox on Exchange? 

Thanks for any assistance.

What is the max number of messages allowed in exchange 2016 / outlook 2013?

Exchange is the server side of a collaborative application product that is part of the Microsoft Server infrastructure. Exchange's major features include email, calendaring, contacts and tasks, support for mobile and web-based access to information, and support for data storage.

Exchange

Microsoft Outlook is a personal information manager from Microsoft, available as a part of the Microsoft Office suite. Although often used mainly as an email application, it also includes a calendar, task manager, contact manager, note-taker, journal, and web browser.