Office365 Send Mail Fails With Irresolvable Conflict

Send Mail: Code: ErrorIrresolvableConflictMessage: The send or update operation could not be performed because the change key passed in the request does not match the current change key for the item.

Note: This is a known issue and it is going to be resolved in the Office365 activity package version 1.15.0.

To be able to see these packages,

  1. Go to Manage Packages
  2. Select the Office365 package
  3. Check the option "Include Prerelease" (as in the example below)
  4. Upgrade the package to a version over 1.15.0.