One option is to go online and mark the Important folder to be hidden. Another option is to unsubscribe from within Thunderbird

That's a "gmail thing' and I ignore it.

My comments also apply to the Allmail folder, in case you're subscribed also to it.

Thank you for responding. I right clicked on "Important" folder and unchecked "Include messages...". Doesn't seem to have done anything. I don't know how to "go online and mark...". Sorry, never had to do that.

highlight the account in folder pane Rightclick and select subscribe in next window, untick Important (and also Allmail, unless you actively NEED that folder)

Thank you. Worked perfectly. Somehow I had 2 "draft" folders, fixed that as well.

Thanks for the feedback. I'm glad all is well. :)

FWIW, "online" you can choose what is shown by Gmail in IMAP (Thunderbird). Go here in your browser: https://mail.google.com/mail/u/0/#settings/labels

I have very recently installed Thunderbird as my default email client. I was interested to se the two folders "important" and "Follow-up" that appeared in my account and today, after having some difficulty in locating a particular email in my inbox I closed the email and thern dragged it from the inbox list to the Important folder. It has completely disappeared from my inbox and is not in the Important folder. Having checked the adjacent folders, including Deleted fruitlessly I then Right Clicked an unimportant email and left clicked "Move to Important". The count increased from 48 to 49 but when I clicked on the Important Folder it was not there and the count reverted to 48.

I have also tried using (right click+left click) to move an email to the (empty) Priority folder and that DID work after a delay of a couplr of ninutes. That particular one is now duplicated in my Inbox. . I've used the same process again to move the same email to Important and this time it worked immediately and I now have three "copies" of that one.

The behavour does not seem to be consistent !

HELP! What did I do wrong earlier and how do I recover my important email? Or must I ask the sender to send it again?

Grateful for any advice

You did not tell us the email domain involved.

Sorry - didn't realise that was relevant. It's a private family domain, let's call it smith89.net, controlled by my son and which I understand is routed via gmail servers. My individual email address would be ron@smith89.net. I also have an individual email account which I use for purposes where I am likely to be bombarded by promotional emails rather than personal mail. I use IMAP for incoming mail. BTW - althouh I am still reasonably competent(?) in these matters I am in my mid 80's so can make mistakes but not with a simple drag and drop!. I do wonder if the relevant imortant email disappeared because I dragged it rather than right click - move - choose destination account and folder in submenu - left click ? was merely dragging wthin in the folder list, having taken the precaution of closing the email first.

Gmail is a world of its own and causes many headaches, such as having this 'Important' folder, that is a duplicate of other folders, and there is the god-awful Allmail folder that has its own bag of worms. I asked about domain for that reason. I cannot answer your specific issue, but remember that, with Gmail, all messages are in one real folder — Allmail. Thunderbird imitates it, but creates real folders - inbox, sent, etc. So, whatever you have in any folder is also in inbox. an whatever you delete from allmail is deleted elsewhere. My personal suggestion is to use only folders that you create, not the Gmail folders. Also, the allmail folder is not recommended for general use, due to its duplication of everything. If you have the Allmail and Important folders, you are paying a price of longer send and receive times, plus an almost doubling of disk space. Just my two cents... :)

Thanks for your advice. Are those folder names special or does the same behaviour apply to any folder that I choose to create on a Gmail server or including my smith89 domain? In other words, would I get the same duplication if I created a folder called “Special” in Thunderbird? And would you regard drag and drop between folders as a dangerous practice? Is the facility to move an email to another account unique to Thunderbird? In the past I’ve always forwarded to myself.

All I can share are my experiences with Gmail. Unlike other email providers, Gmail exerts some control over mail. So, I avoid using Gmail folders other than inbox and sent. You should not experience duplication with other folders, although Gmail may place a copy in the Important folder. My recommendation is to unsubscribe from Important and from Allmail. That saves cpu resources, disk resources, and network resources. Drag and drop on an IMAP account always has a bit of risk because you're moving data across the internet. But I do it regularly. BUT, dragging and dropping to another account will work, but at a higher level of risk. Consider, thunderbird loses control of a message once it initiates a move. Copying is safer because you are assured that nothing will be lost. And maybe I'm too conservative. This process and risk applies to all email clients.