So i am returning custom status code from the autoIT script if the step passes :
Here WinActivate returns zero if the step failed ( means the window is not present)
I'm not that fluent in AutoIt, but the issue here I see with SMTP and step validation. There is no way you can check different inbox for incoming mails, because mail can be received even few days later (which happens rarely, but specs allows it).
The easy way would be:
Send email via addon
Go to outgoing emails folder in Outlook and check if it's present ...