There are three issues seen in this scenario:
Error 1:
If there is an exception when "_MailApproval_ProcessMail_MakeDecision", the error message is not output with.
Cause: Raise the message lacks the placeholder "{0}".
Error 2:
If the regular expression does not match, and the mail is not processed, it is not affected are in the Inbox.
A shift / deletion of mail only happens if it has been edited.
Thus, the mail is checked every run again and is again ignored.
Completely ignored mails should also disappear from the Inbox.
Error 3:
The identification of Approvers done ONLY using the mail address of the sender of the mail.
If there are several people with identical Default Email Address (can as the Main / Sub-identities be the case), the wrong person could be determined and the Make Decision fails.
In addition to comparing the Default Email Address should be checked that the person is not included in this order for this step in PWOHelperPWO.