outlook for Mac fixing sync messages

Jorge D. Guzman 0 Reputation points
2026-09-14T01:09:49.12+00:00

The new outlook for Mac is a complete mess. When a get a new e-mail with an attachment and try to opened I get a message that says: "Need redownload attachments from the server. Please try later". How can a fix that? Also all the e-mails sent stay in the outbox carpet.

Outlook | MacOS | New Outlook for Mac | For business
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  1. Jade Ng 15,480 Reputation points Microsoft External Staff Moderator
    2026-09-14T02:08:36.04+00:00

    Dear Jorge D. Guzman,

    Based on your description, the error "Need redownload attachments from the server. Please try later" together with sent emails remaining in the Outbox may indicate a synchronization or authentication issue between Outlook and the mail server.

    To help narrow down the issue, could you please let me know:

    1. Is this happening with all emails and attachments or only specific messages?
    2. Are you using a Microsoft 365/Exchange account, or another type of account (IMAP, etc.)?
    3. Does the same issue occur when accessing your mailbox through Outlook on the web?

    In the meantime, please try the following steps below and check if it works:

    1.Update Outlook for Mac

    • Open any Office app or Outlook
    • Select Help > Check for Updates

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    • Install all available updates
    • Restart Outlook

    2.Force a sync:

    • Go to Tools > Sync
    • Allow Outlook to complete the synchronization process
    • Once sync is completed, test opening the attachment again and verify whether emails are sending successfully from the Outbox

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    3.Sign out and re-add the account

    • Open Outlook for Mac.
    • Select Tools > Accounts.
    • In the list, select the account you want to remove from Outlook.
    • Select the Manage option and select Remove Account.

    Manage_menu_AccountSetting SignOut_image

    • Select Continue.

    4.Clear Outlook/Microsoft credentials from Keychain

    • Quit Outlook and all Office apps
    • Open Keychain Access
    • Search for entries containing: Outlook/Office/Microsoft/ADAL/Exchange
    • Remove the related credentials
    • Restart the Mac
    • Sign into Outlook again

    5.Test with a new macOS user profile

    Please create a new macOS user profile and test whether the same issue occurs under that profile. You can follow the guidance here: New user or group setup on Mac

    Disclaimer: This link is shared by community members for your convenience. It points to a third-party site that is not managed or verified by Microsoft. We can’t guarantee the quality, safety, or suitability of any content or software found there. Please review carefully and make sure you understand any potential risks before using it.

    If none of the above solutions work, please let me know. Thank you very much for your valuable time and your cooperation.

    I am looking forward to your update.

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  2. AI answer

    2026-09-14T01:10:05.8466667+00:00

    For the sent messages stuck in Outbox in Outlook for Mac, there is a documented cause and fix when Outlook shows Unexpected data was encountered: Outlook cannot locate and use the Sent Items folder because the mailbox folder hierarchy is corrupted. In that case, reset the default folders using one of these methods:

    1. Use Outlook Web App to rename default folders
      • Exit Outlook.
      • Sign in to Outlook Web App.
      • Go to Settings > Options > General > Region and time zone.
      • Change the language, select the preferred date and time format, select Rename default folders so their names match the specified language, and save.
      • If the preferred language is already selected, switch to another language, save, then switch back and save again.
      • Exit Outlook Web App and restart Outlook for Mac.
    2. If Outlook for Windows is available, run /resetfolders
      • Exit Outlook.
      • Open Run.
      • Run: 
             Outlook.exe /resetfolders
    3. If an Exchange administrator is available, the mailbox default folders can be reset with Set-MailboxRegionalConfiguration.

    For Outlook for Mac sync issues more broadly, these checks are supported:

    1. Make sure Outlook is online
      • In Outlook for Mac, on the Outlook menu, confirm Work Offline is not checked.
    2. Check the Exchange account connection
      • Go to Tools > Accounts.
      • Check the Exchange account in the left pane.
      • If the connection indicator is orange, there is a connection problem.
      • If needed, test the same mailbox in Outlook on the web to confirm the mailbox itself is working.
    3. Empty the cache for the affected Exchange folder
      • This can help when Outlook cache corruption causes synchronization problems.
      • Caution: Emptying the cache deletes any information not synchronized with the Exchange server, including contacts' mail certificates. Back up Outlook information first if needed.
      • Steps:
        • Make sure the Mac is connected to the Exchange server.
        • In the navigation pane, Ctrl+click or right-click the Exchange folder.
        • Select Properties.
        • On the General tab, choose Empty Cache.
        • Outlook will re-download the items from the Exchange server.

    For the attachment error “Need redownload attachments from the server. Please try later”, the available context does not provide a specific documented fix for that exact message in New Outlook for Mac. The supported actions in the context that align with sync-related attachment problems are:

    • verify Outlook is online,
    • verify the Exchange connection in Tools > Accounts,
    • test the mailbox in Outlook on the web,
    • empty the cache for the affected folder.
    AI-generated content may be incorrect. Read our transparency notes for more information.

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