Top Known Issues in Microsoft Outlook for Mac – [2025 Update]
Many Mac users frequently encounter recurring problems while using Outlook. While keeping the app updated often resolves most of these issues, some situations may require additional troubleshooting steps. In this blog, we’ve highlighted several of the most common challenges users experience and provided practical solutions to help fix them.
Outlook is a widely used email client developed by Microsoft, designed to handle daily email communication. It allows users to manage messages from multiple accounts within a single interface, offering features that have made it the preferred email application for many Mac users. However, despite its advantages, some users meet recurring problems—such as sign-in errors, calendar sync failures, and other technical glitches. If you’re facing similar issues, this post offers straightforward solutions to help you resolve them. Let’s dive into a detailed look at the most common Outlook for Mac issues and how to fix them.
#Issue 1: “Reply,” “Reply All,” and “Forward” Buttons Not Working
At times, essential functions like Reply, Reply All, and Forward may stop responding in Outlook for Mac. This issue is commonly linked to outdated Office editions. Updating the latest release often resolves the problem.
Follow these steps to check for and install the latest Office updates:
#1- Open any Office app (e.g., Microsoft Word). From the top menu, tick Help and pick Check for Updates.
Note: If the Check for Updates option isn’t visible, you may need to install or update the Microsoft AutoUpdate Tool first. Once updated, repeat this step.
#2- In the Microsoft AutoUpdate window, enable Automatically keep Microsoft Apps up to date. This ensures you receive future security patches and feature improvements automatically.
#3- Press Update to begin downloading and installing any available updates.
#Issue 2: Attachments and Inline Images Fail to Send with Signed or Encrypted Emails
In some cases, users may experience issues when sending signed or encrypted emails using the new Outlook Mac. Specifically, attachments and inline images may fail to transfer properly. This problem is known to occur in certain builds of the new Outlook experience.
Solution: The issue has been addressed in Mac Outlook version 16.66. Updating this edition (or later) should fix the error. To check for and install updates, follow the steps outlined in Issue 1.
#Issue 3: Outlook for Mac Becomes Unresponsive When Using the Search Feature
Some users have reported that Outlook Mac freezes or stops responding when attempting to use the Search function. This behavior is often linked to a recent service-side update intended to enhance search performance. Unfortunately, the update may unintentionally cause the application to crash during specific search queries.
Solution: This issue can typically be resolved by reverting to the previous version of Outlook. Once the rollback is complete, the search feature should return to normal functionality. Microsoft is aware of the issue and may provide a more permanent fix in a future release.
#Issue 4: Mac Outlook Crashes during Sync or at Startup
Users have experienced Outlook for Mac crashing under the following conditions:
- During email synchronization
- Immediately after adding a new email account
- When starting the application
- When a calendar event contains a NULL OriginalStart property
In such cases, Outlook often displays a crash dialog and may generate a Microsoft Error Report, recommending the user update their Office client.
Solution: Microsoft has addressed this problem in Outlook for Mac version 16.70 and later. Installing the latest Office updates is strongly recommended to prevent further crashes and ensure overall stability.
#Issue 5: “Account Already Exists” Error When Adding a Mailbox
When attempting to add a shared mailbox using the “Add Email Account” screen in Outlook for Mac, users may encounter the error message: “Account Already Exists.” This typically happens if the shared mailbox is added before the primary account.
Solution:
#1- Close the error message and return to the main account screen.
#2- Check if the primary email account has been added. If not, add it first.
#3- Once the main account is successfully added:
- Go to Outlook > Tools > Accounts > Delegation and Sharing.
- Click on Shared with Me.
- Select the plus (+) icon at the top-left corner.
- Choose Add the shared mailbox from the list.
#Issue 6: Error 17099 or 3253 When Sending Emails with Attachments
Users may see Outlook Error 17099 or 3253 when trying to send emails that include attachments. This issue often stems from conflicts caused by Norton Security 8.6.3 or later, particularly its Vulnerability Protection module.
Solution:
- Apply the latest Norton Security hotfix, which addresses compatibility issues between Outlook and the Norton module.
- Alternatively, temporarily disable the Vulnerability Protection module (if the hotfix is not yet installed) to verify if it resolves the issue.
#Issue 7: Unable to Open Attachments Due to Helper App Permissions
In some cases, Outlook for Mac displays an error such as: “filename.ext” can’t be opened because you don’t have permission to view it. This typically occurs on systems running macOS 11.6.6, and is caused by a helper app (e.g., Preview) interfering with file access.
Solution:
- Update macOS to version 11.6.7. This update includes fixes for known file permission conflicts.
- If updating is not possible, close the associated helper app before trying to open the attachment.
For example, if you’re opening a PDF and Preview is the default viewer, quit Preview first and then try reopening the file via Outlook.
#Issue 8: Unable to Create or Access Signatures in Outlook for Mac
Following the installation of Office for Mac update 16.63, users may find that:
- The “+” (plus) icon for adding new signatures is unresponsive.
- Existing email signatures are missing or inaccessible.
Solution: Upgrade to Outlook for Mac version 16.64 or later. This update restores access to signature creation and recovers previously configured signatures.
#Issue 9: Email Header Fields Appear Compressed or Shortened
After updating Outlook for Mac to version 16.57, fields such as To, Cc, and Bcc may appear unusually short or compressed, making them difficult to read or edit.
Solution: Install Mac Outlook Beta Channel edition 16.58 (Build 220106) to resolve the layout issue. This version restores proper formatting for message header fields.
Final Thoughts and Additional Support
In this technical guide, we’ve outlined several common issues faced by Outlook for Mac users ranging from broken search functionality and sync errors to problems with attachments and missing signatures. Most of these can be resolved by installing the edition Outlook or macOS updates, as Microsoft continues to release patches addressing known bugs.
However, if you’re still facing persistent issues especially related to OLM file access, corruption, or migration consider using an outstanding tool like CubexSoft OLM Converter for Mac & Win OS. This reliable utility enables you to convert OLM files into over 20 popular formats, including OLM to PST, PDF, MBOX, ICS, HTML, MHT, DOC, EML, CSV, RTF, DOC, vCard, Gmail, Office 365, G Suite, IMAP, Yahoo, Hosted Exchange Server, Windows Live Mail, Zimbra, IBM Verse, Lotus Notes, Amazon WorkMail, and so on.
The software offers a free demo pack, allowing you to test its functionality by converting the first 25 .olm items at no cost. It’s a helpful solution for those needing a smooth, error-free conversion or backup process.
