ayi Seeing as this is the office365 subreddit I assume you're connecting to Exchange online? If so, then you need to upgrade your outlook to a supported version. Technically Outlook 2016 is no longer supported connecting to Exchange online. https://learn.microsoft.com/en-us/deployoffice/endofsupport/microsoft-365-services-connectivity#older-office-versions-not-supported-for-connecting-to-microsoft-365-services https://old.reddit.com/r/sysadmin/comments/14ls8cn/outlook_2016_exchange_online_eos_102023/
