I've never heard of such a case and the fact that it happens randomly makes it even harder to troubleshoot. How sure are you that the messages get sent in the first place? Gmail smtp servers automatically save a copy of all sent messages in the Sent folder of your account. Check if the responses that were never received were actually saved in the Sent folder of your account. Do this via webmail, not Thunderbird. While you're at it, check if the Drafts folder in webmail and Thunderbird have those responses.

The fact that a newly crafted message gets sent and delivered as expected, every time, confirms that Thunderbird is configured and fuctions as expected, as far as sending of messages is concerned.

@Stans -

Thank you for responding to my question - Really appreciated it!

I checked my sent folder via webmail (not Thunderbird) and indeed the email that was not delivered did appear there. Therefore it appears both in the sent folder via webmail (RackSpace email) and also in the sent folder in Thunderbird.

The drafts folder has nothing in it, so that's not the issue.

Therefore still confused, but as you say, it's difficult to determine the issue since it does appear to be intermittent, unfortunately.

If you have any other suggestions, please let me know. I've been using Thunderbird for a few years now and never experienced this.

Regards, Simon

You could get in touch with your email provider and see if they could check the outgoing server logs to see exactly what happened to the non-delivered responses. If you're using IMAP in Thunderbird, it's possible that the RackSpace outgoing server never sent the messages for some reason. Thunderbird by default saves a copy of sent messages in the IMAP sent folder. If this is the case, the presence of a copy in the Sent IMAP folder doesn't necessarily mean that the outgoing server actually delivered the message after Thunderbird submits it to the smtp server. The outgoing server could be discarding the message without issuing any errors due to misconfigurations on the server, but Thunderbird still saved a copy of the message in the Sent folder. You can turn off the saving of Sent messages in Thunderbird, then send a test message via Thunderbird to your Gmail account and check via webmail if the RackSpace server saves that message despite Thunderbird not doing so. This should confirm that the RackSpace outgoing server does it automatically upon successful sending of the message. You can then reply back and forth between your RackSpace account and Gmail to simulate an exchange of messages that would typically happen between you and the affected recipient in a bid to reproduce this problem. Watch out for any error messages displayed by Thunderbird.

Also, does this affect ALL recipients or just a particular one?

Stan,

Ok, I have more information that may be helpful to solve this issue.

I contacted RackSpace and they informed me that even though they also noticed the email (that was not delivered) in the "Sent" folder, there was no log information regarding the actual email on their end. They are under the same impression as you, that the message was moved into the "Sent" folder by Thunderbird, even though the message was never actually sent by Thunderbird to the SMTP server. It appears as though if their SMTP server never actually handled the email, no log information was recorded... As you say, due to IMAP, the message just "appears" to have been sent since it's in the "Sent" folder...

I've used two different SMTP settings and BOTH have the same issue for the SAME email I try to forward. The SMTP servers are for different servers (different companies) and both have this same issue. Which tells me that it's not the SMTP server's fault.

Also, if I forward the same email on my Iphone's email client and it sends perfectly every time (for both SMTP server settings). Also, when I use the RackSpace webmail interface, then it also sends the message every time... So the only conclusion from both the RackSpace support person and myself is that there appears to be some type of miscommunication between Thunderbird and the SMPT servers - And since this only happens with the Thunderbird client, it must be a Thunderbird issue.

Maybe this is something that the developers can look into further? Is there anything else I can provide to assist you in this regard?

If it's happening to me, then it may be happening to others as well one would think... Maybe they just did not reach out to troubleshoot the issue? Again, it only appears to happen when I forward certain messages - It does not seem to be specific to any particular email that was sent to me.

Thanks again for your persistence in trying to resolve this issue.. Any further help would be appreciated!

Regards, Simon

Stan,

More information that may help to solve my issue:

When using my laptop, MacBook Pro and Thunderbird, I have exactly the same issue as on my desktop. The SMTP settings etc. are the same on both computers.

Simon

Hello,

the same thing happens here with me at the MAV Tecnologia provider.

A user sent a message using thunderbird, that message was saved in the sent folder, however, it was not delivered to the recipient.

When analyzing the server logs, no authentication attempts were found on the SMTP server at the time the message was saved in that user's outbox, which ensures that the message was not actually sent.

I would like to know why the message was saved in the sent folder but in fact it was not sent, can this really happen? Is it a bug or other common reason?

Grateful.

@rayanmaia

Thanks for your comment - I still have not solved this issue so hopefully someone out there will eventually figure out what's going on...

Now when I forward an email I always copy another Gmail address I have and check to ensure it's delivered there - That way I know the email was indeed sent! But there must be a better solution I'm sure!

Simon