Right-click the account in the folder pane, Subscribe..., Refresh, and see if you can check (subscribe) the missing folders.

thank you, worked perfectly!

I tried this 'solution', however, my sub-folders did not show when I went to Subscribe, making it impossible for me to 'Refresh'. What do I do now?

gabbycleo said

I tried this 'solution', however, my sub-folders did not show when I went to Subscribe, making it impossible for me to 'Refresh'. What do I do now?

You should first click Refresh to update the list of folders that are defined on the IMAP server, then check the boxes for the folders you wish to subscribe to in TB.

Working in Gmail is a 'less than user friendly activity' for me! How do I Refresh the labels in Gmail (I assume that's what you mean)?

If you open the Settings for the account on the gmail website, there is a section, Labels, where you can enable 'Show in IMAP', which should ensure folders can be subscribed in TB. There is more information about labels and TB in the Labels section here.

I have checked Gmail as you suggested, all folders are ticked to 'show' for Imap & Imap is 'Enabled' Logged into Thunderbird subsequently, still no sub-folders visible to facilitate the 'Refresh' & 'Subscribe' activities you advised. Double-clicked on 'Inbox' & sub-folders appeared one by one, however, when I clicked on a sub-folder to check its content, it was empty & this error message appeared; "The current operation on 'General' did not succeed.The mail server for account xxxx.xxxxxx@gmail.com responded [Non-existent] Unknown mailbox:imap.gmail.com/Inbox/General(failure)." Your further help would be appreciated.

Just to back up a bit, before you added the account to TB, did you enable access by 'less-secure apps' on the Google account webpage? Are cookies for google,com allowed in TB Tools/Options/Privacy? Was the account added with these settings: imap.gmail.com on port 993, SSL/TLS security, OAuth2 authentication?

Just to inform you that I have been using Thunderbird without issue for at least 3 years, until I changed my password after a 'prompt' message from Google in Feb'19 saying they had detected 'unusual' logins. In answer to your questions;

• Did I enable access by less secure apps - No, it was working perfectly previously without this?
• Are cookies for google.com allowed in TB Tools/Options/Privacy? - Yes.
• Was the account added with these settings: imap.gmail.com on port 993, SSL/TLS security, OAuth2 authentication? - Yes.

When you changed the password, did you remove or edit the old one in Tools/Options/Security/Passwords/Saved Passwords?

Attempting to fix this issue on 24Mar'19, I deleted the old password then T/bird added the new password & I saved it. Still no joy!

Try enabling less-secure apps access and see if it makes any difference. You can always reverse the setting if you're convinced it isn't relevant to your problem. Note this is not the same as two-step verification.

In Gmail there is help to find the 'Less secure app access panel';

 "1.Go to your Google Account.

   2.On the left navigation panel, click Security.
   3.On the bottom of the page,in the Less secure app 

access panel, click Turn on access.

        If you don't see this setting, your administrator might have turned off less secure app account access."

1. Did that. 2. Not visible, therefore cannot initiate. 3. Not switched off by Administrator.

Where do you suggest I go from here to fix things?

If this is a private account, not a G-Suite account, there is no administrator to reinstate your ability to enable access by less-secure apps. But, as I understand it, in this case, the absence of the option in Security settings means that you must have enabled 2-step verification. So, to access the account from TB, you must create an app password and enter it in TB in place of the normal account password. That, together with OAuth authentication, should allow TB to access the gmail account.

https://www.slipstick.com/outlook/outlook-gmails-secure-apps-setting/

https://support.google.com/accounts/answer/185833?hl=en

This is a shared family PC, my other half has 'Administrator' status for the OS via our Microsoft Account. I am certain we have not enabled 2-step verification. We have not enabled 'access by less secure apps', as informed previously. However, whilst awaiting your latest response, I felt sure the problem lay in the configuration of 'labels' link between Gmail & Thunderbird. I considered that the easiest way to resolve where the problem lay & 'apply a fix', was to remove the account from Thunderbird, then activate a new account (albeit using the same email address & password) thereby allowing Thunderbird to 'fix itself' by recreating the necessary linkage to Gmail automatically. After closing Thunderbird & then re-activating it, I'm pleased to advise this method resolved the problem. Thanks for your time & effort in attempting to identify my issue & provide a fix, hopefully my solution will serve to help others without the need to reduce their security.