Errors when sending emails from security groups, distribution lists, or mail-enabled Public Folders in Outlook for Mac

Original KB number:  2739937

Symptoms

When you try to send email messages from a distribution list, a security group, or a mail-enabled Public Folder, Outlook for Mac 2011, Outlook 2016 for Mac, or Outlook for Mac 2019 times out, and you receive one of the following error messages:

Error: An unknown error has occurred in Outlook.
Details: Mail could not be sent. The message has been moved to your Drafts folder.
Error code: -19991

Error: An unknown error has occurred in Outlook.
Error code: -19992

Error: An unknown error has occurred in Outlook.
Details: Mail could not be sent.
Error code: -21999

Cause

Outlook for Mac has the following limitations:

• You can't send email messages from a distribution list, a security group, or a mail-enabled Public Folder.
• You can't use a distribution list, a security group, or a mail-enabled Public Folder as a delegate.

Workaround

To work around these limitations, take the following actions:

• Send email messages from a single account instead of from a distribution list, a security group, or a mail-enabled Public Folder.
• Use single accounts as delegates instead of using distribution lists, security groups, or mail-enabled Public Folders as delegates.
• Use a Microsoft 365 Group instead. For more information about Microsoft 365 Groups, see Learn about Microsoft 365 Groups.