Use Your Own SMTP Server is NOT a Beta
The feature lacks the basic functionality of detecting a rejected connections from an SMTP server.
Repairshopr will make it appear as though the message was sent, but the recipient will never receive it.
With Google's SMTP server, that rejection will trigger about 400 emails into a Marketr campaign.
Message send failure detection / notification is a basic and expected function for a feature like this. A Beta is supposed to be feature-complete with bugs to work out. The feature is pre-alpha at best, and users should be aware of the possibility that their messages may appear to have been sent when were not before opting in to testing.