Users did not receive email from workflows, logs show ErrorMessageSizeExceeded

Problem

Users did not receive emails supposed to be sent from a process instance. The following error was logged in the HostServer logs:

SourceCode.Workflow.Common.EWS: Exchange error code: ErrorMessageSizeExceeded Exchange error: Microsoft.Exchange.WebServices.Data.ServiceResponseException: The message exceeds the maximum supported size., Cannot save changes made to an item to store.

Solution

'ErrorMessageSizeExceeded' is response code returned by Exchange.

According to Microsoft:

https://learn.microsoft.com/en-us/exchange/client-developer/web-service-reference/responsecode

This error indicates that the message that K2 is trying to send exceeds the allowed limits.

Check the size of the attachment your process instance is attaching to the email. If it is too big, try reducing the attachment size or remove the attachment and try again.