Can you exclude that someone else just hit "send" in your absence or just moved the message to "sent"?

There was no one else in the office at the "sent" time on the e-mail.

Control+Enter(Return) is the shortcut for Send. Any change you hit that by mistake?

I should have reported that I was out of the office when it was transmitted.

klyerly said

I should have reported that I was out of the office when it was transmitted.

Hm, how then do you know that there was nobody else? Would it be possible for someone to enter and leave before you return without you noticing?

And: was your screen locked?

I am asking because it seems highly unlikely that TB sent the email without any user interaction.

My daughter and I were the only people in the house at the time and we were watching a basketball game. If it is not an issue with TB then we have ghosts in the machine.

klyerly said

My daughter and I were the only people in the house at the time and we were watching a basketball game. If it is not an issue with TB then we have ghosts in the machine.

Maybe not ghosts. The only potential reasons apart from human intervention for what you wrote I can think of off the top of my head:

• Some TB extension sending message.
• Malware on your machine (Windows? Do you have current AV software running?).
• Some weird bug in TB.