Your issue is with the owl add-on, I would not suggest trying to over ride what they have disabled, as doing so might cause other unwanted actions. This whole exchange client thing is very fragile, so deviation from the path is not a good idea I would guess.

Having said that, I don't know why they did not deselect the option and then disable it as it is a "feature" of Microsoft Outlook web stuff that they insist on putting a copy of outgoing mail in your sent folder. They have no opt out at all.

Thank you. The Owl support folks responded and advised:

Please check in Thunderbird account settings | SMTP servers whether you have any SMTP servers related to this email address or server. If so, please delete them. You might unknowingly using one of those. Owl doesn't use SMTP.

They were correct.

I deleted the SMTP records but still had problems.

The error messages I got indicated that Thunderbird was still attempting to use SMTP even though I had removed all SMTP references to this account. I decided that it must be an Owl problem having something to do with the configuration of the account. I then removed the account from Thunderbird and pulled up the Owl for Exchange page under Add-ons in Thunderbird and chose Options. Under Mail account management I chose the Add new account manually... button, filled in the choices in the Add new Exchange account window and then clicked on Create account.

The account was created and the problems were gone! Prior to this I had created the account using Add Mail Account under Account Actions in Account Settings rather than through the Owl interface. This appears to be the source of my problem.

I thank Matt for his response, and the Owl folks, both for their assistance and their product, which is now working, quite crisply, for me.

The only problem issue I experience now is that, sometimes, upon initiating Thunderbird, the Exchange account will not attach, i.e. the busy icon continually rotates and no messages are retrieved. I have been able to resolve this each time by exiting Thunderbird and restarting.

I would strongly encourage you to post that information with the owl folks. As they are also responsible for the new account wizard in Thunderbird and have done most of the changes to it in the past few years they would be best placed to fix any issues that arise from the installation of the add-on and subsequent use of the account or your apparent hangs on startup.

Thanks for the recommendation. In fact, I shared my experience with account creation with them before I posted it here. They expressed their thanks. I will mention the hangs on startup to them as well but wanted a little more experience in order to determine if it would persist. It happened to me again today.

I have the same problem, but the Owl email account I have on Thunderbird has no SMTP settings associated with it. I do use Thunderbird with 2 other email accounts though, both of which use SMTP of necessity for outgoing mail.

I have noticed that the duplicate messages also appear in the Sent Mail on the Exchange server when I log into MS Outlook directly on line. However, if I send a message when on line, it is not duplicated in the Outlook Sent Mail folder.

Does anyone have any further suggestions? Meanwhile I will contact Owl (Beonex).

Anthony Sheppard

For a long time outlook.com has made copies of mail being send and placed than in the sent folder. I would guess it does the same for office365, but the owl addon does not have an option not to place a copy in the send folder.

But I have never used the add-on. So everything I say about it is a guess.