does it really send two, or just add two to the sent folders (this is normal if you use Gmail or Outllok.com as they add the mail to the server sent folder as it goes out through their servers and Thunderbird add it to the local sent folder when you click send, then imap synchronises and you have two.

The easiest way to fix it is to tell Thunderbird not to save a copy. Right click the account in the folder pane, select settings and in copies and folders for the account turn off the save feature for sending mail.

I said easiest way, but it is really the only way as neither provider offer a way to opt out at their end.

I appears to really send 2 e-mails since when you go to delete them the total Kilobytes for the 2 e-mails is way up, like double for just 1 e-mail.

Thanks, belton1970@outlook.com

Does the recipient get 2 emails? That is the question. Matt told you how to stop getting 2 copies saved to your sent folder. That is the usual issue.