Unless you have manually created a filter to move an email, Thunderbird will only move a message if it thinks it's spam. So, the first place to look would be in your Spam/Junk/Bulk and Deleted folders.

Next thing go check would be your Junk Settings, which can be found in two places:

- Global settings are found (in Windows) in <Tools | Settings | Privacy & Security | Junk>. There you have the choice for messages classified as spam/junk to be moved to the Junk folder or automatically Deleted. Similar setting per account are found in <Tools | Account Settings | Junk Settings | Destination and Retention>.

Another thing to consider is that your email provider may be flagging the message as spam before Thunderbird ever sees it. If possible, when you are expecting to receive one of those messages, close Thunderbird and check your webmail and see if the message ever appears there in its Spam folder. I usually disable my providers spam detector, if possible, and let Thunderbird handle it.

I have many times been expecting those kinds of confirmation emails but the took several hours or more to arrive... if ever. That indicates a problem with either the sender or your email provider. You have no control over that.

I wrote a reply to my problem / Lin's response but I don't see it here. Thank you Lin for your robust response. - - - I did find my missing security code emails in TRASH - - - So somehow T-bird is sending them to trash.