How to fix a mail sync issue between Outlook and Gmail

Richard Taylor 20 Reputation points
2026-10-29T16:20:53.59+00:00

I have just installed New Outlook for Mac and successfully added my personal and business gmail accounts to it. However, Outlook does not sync any sent, new or deleted mails. Emails I send via Outlook eventually bounce hours later. I've updated IMAP settings in gmail but still nothing changes. Help!

Outlook | MacOS | New Outlook for Mac | For home
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AI answer

2026-10-29T16:23:02.6133333+00:00

Check the complete Gmail nondelivery report and Outlook’s Sync Errors first, then reauthorize each Gmail account through Google’s sign-in flow; delayed bounces identify a sending failure that changing IMAP settings alone will not resolve.

1. Identify the sending error

  1. Open one of the bounced messages and retain the complete nondelivery report, especially:
    • SMTP error code
    • Diagnostic text
    • Reporting server
    • Original recipient
  2. In Outlook, select Window → Sync Errors and look for entries matching the time the message was sent.
  3. Test a short message with no attachment:
    • Send it from Outlook to another address.
    • Confirm whether it appears in Gmail web under Sent.
    • Send another message from Gmail web to determine whether the problem is limited to Outlook.

If the bounce says SMTP error -3253 or “Connection to the server failed or dropped,” Microsoft currently lists that Outlook for Mac sending problem as Investigating.^1^

Also test without attachments. Gmail accounts synchronized through Microsoft Cloud have a documented 10 MB attachment limit in Outlook, even though Gmail itself permits larger messages.^2^

2. Reauthorize the Gmail accounts

Since adjusting IMAP did not help, refresh the authorization rather than changing the same settings again.

For each affected account:

  1. Preserve any unsent drafts outside Outlook.
  2. Go to Outlook → Settings → Accounts.
  3. Select the Gmail account.
  4. From Manage, select Remove Account, then choose Sign Out On This Device.
  5. Select + Add Account, enter the Gmail address, and choose Continue.
  6. Complete the browser-based Google sign-in.
  7. On Google’s permissions page, select Allow, then finish adding the account.^3^

Use Sign Out On This Device, not Sign Out On All Devices, unless intentionally disconnecting every Outlook client. Microsoft notes that re-adding the account after signing out on all devices can take up to four hours.^2^

3. Check folder exposure, not IMAP activation again

Because IMAP has already been updated, only check whether Gmail exposes the affected folders:

  1. Gmail web → Settings → See all settings → Labels.
  2. Enable Show in IMAP for:
    • Inbox
    • Sent Mail
    • Trash
    • All Mail
  3. Return to Outlook and select Sync on the ribbon.
  4. Allow up to 15 minutes for the refresh.^4^

New or renamed Gmail labels can take up to four hours to appear. Older mail in a large mailbox can take several days to finish downloading, but Microsoft states that new mail should still send and arrive without delay; therefore, mailbox initialization does not explain messages bouncing hours later.^2^

4. Optional isolation test: bypass Microsoft Cloud sync

New Outlook for Mac can synchronize Gmail through Microsoft Cloud. Direct Google synchronization is a supported configuration option, but Microsoft does not document it as a guaranteed fix for this exact failure.^5^

To isolate the cloud-sync path:

  1. Remove one affected account using Sign Out On This Device.
  2. Select Tools → Accounts → + Add Account.
  3. Enter the Gmail address and select Continue.
  4. Select Not Google?
  5. Choose Sync directly with Google.
  6. Complete Google sign-in and select Allow.^6^

Test sending, deleting, and receiving before changing the second account. Direct synchronization may not provide features that depend on storing the non-Microsoft mailbox in Microsoft Cloud.

5. Collect logs and escalate if both accounts still fail

  1. Select Window → Sync Errors → gear icon → Turn on logging for troubleshooting.
  2. Restart Outlook and choose Leave Logging On.
  3. Reproduce one send failure and one delete/sync failure.
  4. Quit Outlook, restart it, and turn logging off. Leaving it enabled causes logs to keep growing.^7^
  5. Go to Help → Contact Support and provide:
    • Outlook build
    • macOS version
    • Complete nondelivery diagnostic
    • Time of the test
    • Whether Gmail web worked
    • Whether direct Google sync changed the result
    • Diagnostic logs

Review logs before sharing them because they can contain email addresses and message content.^7^

References

  1. Fixes or workarounds for recent issues in Outlook for Mac | Microsoft Support
  2. Known issues syncing Google accounts to the Microsoft Cloud
  3. [Legacy Outlook for Mac](https://support.microsoft.com/outlook/add-a-gmail-account-to-outlook-for-mac)
  4. Fix problems connecting your Google account to the Microsoft Cloud | Microsoft Support
  5. Sync your account in Outlook to the Microsoft Cloud | Microsoft Support
  6. Add email accounts in Outlook for Mac using Microsoft Cloud | Microsoft Support
  7. Enable logging in Outlook for Mac
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  1. Richard Taylor 20 Reputation points
    2026-10-29T16:42:13.8433333+00:00

    Solved: Outlook for Mac not syncing two Google accounts (fixed with “Sync directly with Google”)

    Posting the solution in case it helps anyone with the same symptoms.

    The problem New Outlook for Mac (latest build) with two Google accounts: a Google Workspace business account and a personal Gmail. Both connected without errors, but nothing synced in either direction.

    • Mail sent from Outlook never reached Gmail or the recipient. It sat in Outlook’s Sent folder, and Gmail’s Sent folder on the web never showed it.
    • A “We couldn’t deliver your message” notice (failure code 7d1c) arrived many hours later.
    • Stars, deletes and other changes in Gmail on the web never appeared in Outlook.
    • No sync error or warning was displayed.
    • Gmail on the web worked normally, and so did Outlook on my phone.

    What I tried first (none of it helped)

    • Removing and re-adding both accounts, quitting with Cmd + Q, and rebooting
    • Pausing the VPN and adding Outlook to the VPN bypass list
    • Checking Outlook wasn’t set to Work Offline
    • Confirming IMAP was enabled in the Google Admin console and in each Gmail account
    • Ticking “Show in IMAP” for Inbox, Sent Mail, Drafts, Trash and All Mail under Gmail’s Labels tab
    • Checking the Admin console’s API controls (no restrictions, no apps pending review)
    • Re-granting Outlook’s permissions on Google’s consent screen

    The fix New Outlook for Mac syncs Google accounts through Microsoft’s cloud by default. Bypassing that path solved it:

    1. Go to Outlook → Settings → Accounts, select the Google account, then choose Manage → Remove Account → Sign Out On This Device. (Avoid “Sign Out On All Devices”, which can delay re-adding the account.)
    2. Choose Add Account, enter the Gmail address and click Continue.
    3. On the next screen, choose Not Google? and then Sync directly with Google.
    4. Complete Google’s sign-in and allow all the requested permissions.

    I did this for both accounts. Sending, receiving, starring and deleting now sync in both directions, between Outlook and Gmail on the web.

    My conclusion Since everything worked once Outlook talked to Google directly, the fault seems to be in the Microsoft cloud-sync path rather than in the Google account, IMAP settings or domain configuration (SPF, DKIM and DMARC all passed). I can’t say what is going wrong on Microsoft’s side, but if you see the same symptoms, switching to direct sync is worth trying before anything else.

    Trade-off Direct sync may not support features that depend on storing the mailbox in Microsoft’s cloud. I haven’t missed anything so far, but check this if you rely on such features.Solved: Outlook for Mac not syncing two Google accounts (fixed with “Sync directly with Google”)

    Posting the solution in case it helps anyone with the same symptoms.

    The problem
    New Outlook for Mac (latest build) with two Google accounts: a Google Workspace business account and a personal Gmail. Both connected without errors, but nothing synced in either direction.

    • Mail sent from Outlook never reached Gmail or the recipient. It sat in Outlook’s Sent folder, and Gmail’s Sent folder on the web never showed it.
    • A “We couldn’t deliver your message” notice (failure code 7d1c) arrived many hours later.
    • Stars, deletes and other changes in Gmail on the web never appeared in Outlook.
    • No sync error or warning was displayed.
    • Gmail on the web worked normally, and so did Outlook on my phone.

    What I tried first (none of it helped)

    • Removing and re-adding both accounts, quitting with Cmd + Q, and rebooting
    • Pausing the VPN and adding Outlook to the VPN bypass list
    • Checking Outlook wasn’t set to Work Offline
    • Confirming IMAP was enabled in the Google Admin console and in each Gmail account
    • Ticking “Show in IMAP” for Inbox, Sent Mail, Drafts, Trash and All Mail under Gmail’s Labels tab
    • Checking the Admin console’s API controls (no restrictions, no apps pending review)
    • Re-granting Outlook’s permissions on Google’s consent screen

    The fix
    New Outlook for Mac syncs Google accounts through Microsoft’s cloud by default. Bypassing that path solved it:

    1. Go to Outlook → Settings → Accounts, select the Google account, then choose Manage → Remove Account → Sign Out On This Device. (Avoid “Sign Out On All Devices”, which can delay re-adding the account.)
    2. Choose Add Account, enter the Gmail address and click Continue.
    3. On the next screen, choose Not Google? and then Sync directly with Google.
    4. Complete Google’s sign-in and allow all the requested permissions.

    I did this for both accounts. Sending, receiving, starring and deleting now sync in both directions, between Outlook and Gmail on the web.

    My conclusion
    Since everything worked once Outlook talked to Google directly, the fault seems to be in the Microsoft cloud-sync path rather than in the Google account, IMAP settings or domain configuration (SPF, DKIM and DMARC all passed). I can’t say what is going wrong on Microsoft’s side, but if you see the same symptoms, switching to direct sync is worth trying before anything else.

    Trade-off
    Direct sync may not support features that depend on storing the mailbox in Microsoft’s cloud. I haven’t missed anything so far, but check this if you rely on such features.

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