Fixes or workarounds for recent issues in Outlook for Mac

Last updated: June 2026

Outlook for Mac features, add-ins, and known issues

• [INVESTIGATING] Outlook for Mac fails to send email with SMTP error '-3253' or 'Connection to the server failed or dropped'
• [INVESTIGATING] Replying to or forwarding an email does not include the original message in email body in legacy Outlook for Mac
• [INVESTIGATING] Auto-complete suggestion does not work in Outlook for Mac
• [INVESTIGATING] The Detect Language Automatically feature is not working as expected in Outlook for Mac
• [FIXED] When the reading pane is set to one side or hidden, it is not retained upon re-launch in Legacy Outlook for Mac
• [INVESTIGATING] Outlook for Mac and Outlook Mobile intermittently stop syncing
• [FIXED] Inbox shows incorrect number of unread items in Outlook for Mac
• [FIXED] Subject and body are blank when sending S/MIME emails in Outlook for Mac
• [FIXED] Errors CAA2000B, 4usqa, and 49dvs when trying to sign in to classic Outlook and Outlook for Mac
• [FIXED] Legacy Outlook for Mac emails are not grouped in Conversation threads as expected for Exchange OnPremise/Office 365 and Google accounts
• [FIXED] Outlook for Mac stops syncing when Conditional Access is enabled
• [INVESTIGATING] Some Outlook for Mac and iOS users are seeing a generic shadow.outlook.com email when drafting an email
• [FIXED] Some options are grayed out in the attachment dropdown menu in legacy Outlook for Mac
• [FIXED] Unable to add files as an attachment to emails in Outlook for Mac
• [BY DESIGN] Unable to use the Contact Support option from the Help Menu in Outlook for Mac
• [INVESTIGATING] Unable to assign categories to items in Shared and Delegated Mailboxes in Outlook for Mac
• [FIXED] Unable to add an account in Outlook for Mac
• [FIXED] Microsoft 365 for Mac users in the Beta channel are not offered app updates
• [BY DESIGN] Follow Up flag does not work in outgoing emails in legacy Outlook for Mac
• [WORKAROUND] IMAP Yahoo and AOL accounts might experience issues with re-syncing folder content
• [FIXED] Selecting Reply, Reply All, and Forward buttons is not working as expected
• [FIXED] Outlook fails to send attachments and inline images when sending a signed or encrypted email using Outlook for Mac
• [FIXED] Outlook for Mac stops responding when using the search feature
• [WORKAROUND] Outlook for Mac "Account already exists" error

Click here for older crashes and slow performance issues that are fixed

• [FIXED] Attachments missing from emails when using macOS Big Sur
• [FIXED] Can't add M365 accounts in Outlook for Mac when the macOS language is set to Turkish
• [FIXED] Can't create new signatures in new Outlook for Mac and existing signatures are missing
• [FIXED] Calendars don't display in the left pane after upgrading to 16.63 build in legacy Outlook for Mac
• [FIXED] Outlook stops responding when viewing Uber receipt emails and some other emails with tables
• [FIXED] Outlook for Mac fails to open attached files if the helper application is already running after installing macOS 11.6.6 update
• [FIXED] To, CC, and BCC fileds are shortened after updating Outlook for Mac
• [FIXED] Search in Outlook for Mac returns no results after installing macOS Monterey 12.1
• [FIXED] The new Outlook for Mac users cannot access Online Archive mailbox
• [FIXED] Outlook for Mac crashes unexpectedly on startup or during mail synchronization
• [FIXED] Characters are garbled in email body
• [FIXED] Error -17099 or -3253 when trying to send an email with an attachment

Changed functionality and blocked or discontinued features

• The Toggle Button to revert to Legacy Outlook Client is missing in Office 2024 Home and Business for Mac
• New location for key functions and direct access to other Microsoft 365 apps in Outlook for Mac
• Missing toggle button in Outlook for Mac
• Legacy Outlook for Mac 2011 does not work with macOS 10.15 Catalina
• Sending meeting updates with REST calendar sharing feature in legacy Outlook for Mac
• Categories no longer appear in the sidebar of individual calendars in legacy Outlook for Mac
• Known issues syncing Google accounts to the Microsoft Cloud

Need more help?

	To report issues or provide feedback, simply go to Help > Contact Support in Outlook for Mac. For more information, see Contact Support in Outlook for Mac.

Have a feature request?

	To suggest new features in Outlook for Mac, go to Help > Give Feedback. We're listening.