It has come to our attention that selecting E-mail from the Parties screen or Field Level Events, which opens an new Outlook window, is putting the Subject into the To field. This does not affect e-mail merges.
Collection-Master has not changed. Outlook has recently updated and no longer accepts the format that has been used since this feature was created.
If you are using Outlook Version 1912 (Build 12325.20344) the software will work as originally intended.
However, if you are using Outlook Version 2001 (Build 12430.20184) it will exhibit the behavior mentioned above.
This has been escalated to the development team to implement a permanent fix to work with all versions of Outlook.
For now, the workaround would be to simply cut the Subject from the To line and place it in the Subject line. Clients may choose to roll back Outlook to a previously working version.
This has been documented in Knowledge Base Problem ID 004362