New Outlook for Mac – Persistent IMAP Sync, Search & Attachment Failures (MS Support Unresolved)

I am reporting a persistent, reproducible issue with New Outlook for Mac that remains unresolved despite extensive troubleshooting, including two Microsoft Support cases. I am seeking a technical investigation and a permanent solution, not another repetition of basic troubleshooting steps.

1. System configuration

• Application: Microsoft Outlook for Mac (New Outlook)
• Current version: 16.114.4 (tel:26110224); previously 16.114.3
• Operating system: macOS Tahoe 26.7.2 (up to date)
• Email provider: https://mailbox.org/
• Account type: IMAP (not Microsoft Exchange / Microsoft 365)
• VPN: Not in use

2. Problems experienced

The following issues occur repeatedly:

1. Email search fails: Search results remain stuck on grey loading placeholders indefinitely.
2. Attachments cannot be downloaded: Both old and newly received attachments fail, displaying either “Downloading attachments from server…” indefinitely or the message: “Attachments need to be downloaded again from the server. Please try again later.”
3. Extremely slow mailbox loading and synchronization, affecting normal email use.
4. Delays when sending emails, also documented during Microsoft Support troubleshooting.

The problems are intermittent but recurring, making Outlook unreliable for everyday use.

Important: The https://mailbox.org/ webmail interface works correctly, including searching emails and downloading attachments. Microsoft Support also reviewed comparisons with Apple Mail and Legacy Outlook and concluded that the issue appears specific to New Outlook for Mac.

3. Troubleshooting already performed

The following measures have already been attempted, without a lasting resolution:

• Created two new Outlook profiles.
• Removed and re-added the affected IMAP account.
• Performed Outlook account remapping.
• Reset the Outlook account and rebuilt local synchronization data.
• Re-synchronized the mailbox and allowed sufficient time for completion.
• Completely uninstalled and reinstalled Outlook, followed by fresh account configuration.
• Verified internet connectivity and basic account functionality.
• Compared New Outlook with Legacy Outlook, webmail and Apple Mail, as documented in Microsoft Support’s case notes.
• Verified Outlook and macOS versions and checked for updates.
• Retested after account resets, reinstallation and reconfiguration.

Result: The account reset temporarily restored email search, but attachments continued to fail. Shortly afterward, search stopped working again. Both problems persist even with newly received messages.

A separate macOS user profile was additionally suggested by Microsoft Support, but I have no confirmed result from that test.

4. Microsoft Support involvement

I have contacted Microsoft Support repeatedly under different case numbers

During the latest interaction on November 6, 2026, Microsoft Support:

• Reviewed the previous case history and confirmed that extensive troubleshooting had already been performed.
• Acknowledged that the problem appears isolated to New Outlook for Mac.
• Confirmed that available troubleshooting at their support level had been exhausted.
• Could not offer a permanent resolution or a specific software fix.
• Recommended posting the issue in the Microsoft Tech Community and submitting feedback through the Microsoft Feedback Portal.

Similar IMAP-related problems have also been discussed publicly since at least April 2026, without an identified resolution applicable to my case.

5. Request to Microsoft Outlook engineering / product specialists

Given the extensive unsuccessful troubleshooting, I would appreciate specific answers to the following:

1. Is this a known bug affecting IMAP accounts in New Outlook for Mac?
2. Is there an identified issue with IMAP synchronization, attachment retrieval or the search backend?
3. Are there diagnostic logs, error codes or targeted tests that would help engineering identify the root cause?
4. Is there a confirmed fix, reliable workaround or planned software update addressing these symptoms?
5. Can this issue be escalated to the Outlook for Mac engineering team, rather than restarting standard first-level troubleshooting?

This issue has already consumed considerable time across multiple troubleshooting attempts and Microsoft Support interactions, while essential Outlook functionality remains unavailable.

I would greatly appreciate a technically substantiated response, a concrete escalation path and, ideally, a permanent resolution.

Thank you.