MS Outlook on a Mac won't talk to MS 365

Dyer, Charles P 0 Reputation points
2026-10-03T10:24:39.31+00:00

I have an MS Account attached to my .edu email. I have MS Outlook, set Classic, on a Mac mini. I have multiple email accounts set up in Outlook. These included the school email, my work email (both MS 365 accounts) and a gmail account, an Apple iCloud account, and a MS outlook account. All used to work. Now, all work except the school account.

The school account still works on the Mac when using the web interface; I hate webmail. The school account also still works using Apple Mail and Mozilla Thunderbird. The school email works on a Ubuntu system using Thunderbird. The school email works on a Windows 11 system with Thunderbird and with both 'classic' and 'new' Outlook; I'm not fond of 'new' Outlook.

The error message was that Outlook could not contact the server. I deleted the school email account in Outlook on the Mac and then attempted to create a new account. Outlook cannot connect to the server. The school email cannot be reinstalled on MS Outlook on the Mac. By 'cannot connect' I mean that the school email is not automatically recognized as an MS 365 account, and if I try to set it up by hand as a MS 365 account, as an Exchange account, as an outlook account, or even as an IMAP/SMTP account, it is not recognized and cannot connect. If I delete and reinstall other accounts, there is no problem setting them up.

Outlook on the Mac is clearly working. The server at the school is clearly working. The Mac can see the MS server when using the web interface or two different email clients. The school account used to work. I have made no changes to it, but it doesn't work now.

Perhaps someone can explain why an MS email client won't connect to an MS mail service?

Outlook | MacOS | New Outlook for Mac | For education
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  1. Kristen Tran 2,040 Reputation points Independent Advisor
    2026-10-03T11:51:08.44+00:00

    Hi Dyer,

    Thank you for providing such a detailed explanation of the issue.

    Based on the information you've shared, the school mailbox itself appears to be functioning correctly, as you can still access it through Outlook on the web, Apple Mail, Thunderbird, Ubuntu, and even Outlook on Windows. This suggests that the issue is likely specific to Outlook for Mac rather than the Microsoft 365 service or the school's mail server.

    Since you have already removed the account and attempted to add it again, I would recommend the following additional troubleshooting steps:

    1. Make sure Outlook for Mac and macOS are fully up to date.
    2. Clear any cached Outlook credentials from macOS Keychain Access:
      • Quit Outlook and all Office applications.
      • Open Keychain Access.
      • Search for entries related to the affected school account, Exchange, or ADAL authentication tokens.
      • Remove the entries associated with the school account.
      • Restart Outlook and try adding the account again.
    3. Create and test with a completely new Outlook profile. This is different from removing and re-adding a single account, because a new profile creates a separate Outlook environment without reusing any existing profile settings or cached data. For reference: Manage profiles or identities in Outlook for Mac | Microsoft Support

    If the issue persists after testing a new Outlook profile, I recommend reaching out to your school's IT administrator so they can review the account configuration and check whether there are any settings or policies that may be preventing Outlook for Mac from connecting properly.

    I hope this helps point you in the right direction. If you have any concerns, please let me know, and I'll be happy to help further.

    Warm regards.

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