Monthly Archives: November 2025

Office, Outlook 2016, Outlook 2019, Outlook 2021, Outlook 2024, Outlook 365

Outlook error: "The Outlook data file has reached the maximum size"

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If the local Outlook OST or PST file reaches 50GB, you will get the following message in Outlook: The Outlook data file has reached the maximum size. To reduce the amount of data in this file, permanantly delete some items. If you can't delete any items, you can add a value in the Registry to increase the maximum size. For example, to increase the maximum size for a PST or OST file to 100GB, add the following value: HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Outlook\PST MaxLargeFileSize Read more [...]
Exchange, Exchange SE

Exchange SE: Mails stay in the Outlook Outbox

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In on-prem Exchange, some limits are set for the number of sessions a user can open. If the user has many connections to different calendars and mailboxes, these limits can be reached. On the Exchange server, in the Application Event Logs, you can see entries like this: EventID 9646 - Mapi session [..] with client type WebServices exceeded the maximum of 16 objects of type Session. or EventID 9646 - Mapi session [..] exceeded the maximum of 32 objects of type Session. These 2 errors cannot be Read more [...]