You can increase the limit for the nickname cache.For information about how to do this, see Remove AutoComplete list entries one at a time. You can proactively remove AutoComplete list entries that you no longer need.To avoid this situation, you can use the following general approaches: Therefore, you might find that some names are unexpectedly removed from your nickname cache. It does this based on the process of usage weighting. After you reach this limit, Outlook uses an internal algorithm to determine the best names to remove from the list. Outlook limits the number of entries that you can save in the AutoComplete list. This app maintains its own AutoComplete list.

Note: The AutoComplete list for Outlook is specific to Outlook and is not shared with Outlook on the web. The list contains SMTP addresses, LegacyExchangeDN entries, and display names for people to whom you have sent mail previously. The AutoComplete list, also known as the nickname cache, is generated automatically when you send email messages from Outlook. The list is used by both the automatic name-checking feature and the automatic completion feature. Microsoft Outlook maintains the AutoComplete list. In this specific scenario, only two sections of this article apply: “Enable the AutoComplete feature” and “Remove AutoComplete list entries one at a time.” Beginning in Outlook for Microsoft 365 Version 2202 (Build 14931.20604), if you’re connected to an Exchange Online mailbox, the suggestions list for the To/Cc/Bcc lines when you compose a message is powered by Microsoft Search. Exchange Online provides some search features through Microsoft Search.

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