Assegnate 3 su 5 stelle
My opinion is based on the discovered error: does not save sent copy in Sent, nor in Sent in local folders, also, no chance to set the exact sending time.
Eventually, I checked the native TB option through Menu > Send unsent messages, and it works smoothly, saving a copy in the Sent folder of the acount from which the email was sent.
The button provides NO own send functions. It only calls the native send now function. If the mails are not saved, then the native function has an issue.