If you want to see all folders all the time, disable this feature.

The visible folders that you see in Thunderbird are controlled by 'subscriptions'.

You can enable or disable the subscription feature. If it is disabled, you will see all folders, including normally-hidden system folders. You might choose to only see a certain set of folders for performance or convenience or simplicity of the display.

You can enable or disable the subscription feature within Thunderbird by clicking on:

Tools → Account Settings → Server Settings → Advanced → Show Only Subscribed Folders

Once the subscription feature is enabled, you can manage the 'visible' or subscribed folders by clicking on:

File → Subscribe

from within Thunderbird. Select all IMAP folders that you want to be visible.

Many people find the display of deleted messages in IMAP accounts to be confusing.

Essentially, deleted items are not actually deleted, they are 'marked for deletion' (for speed) but are not actually deleted until an 'expunge' operation occurs (also referred to as a 'compact' operation). To further confuse users, each mail client has its own way of handling messages marked for deletion.

In Thunderbird, you can click File → Compact Folders to compact all folders.

You can also right-click on any folder and choose 'Compact' to expunge that folder (quicker on large mail stores).

There is also a setting to automatically expunge the Inbox folder upon exiting Thunderbird:

Tools → Account Settings → <account> → Server Settings → Cleanup/Expunge Inbox on Exit

Deleting messages with an IMAP mail client is a little different than deleting messages in a POP mail client. Most POP mail clients will actually move deleted messages into another mail folder. While this is convenient and fast with a local mail store located on your own PC, it is another matter with a server-based message store.

To change how deleted mail is handled, go to:

Tools → Account Settings → Server Settings → When I delete a message

• By default it is set to “Move it to the Trash Folder”.
• If “Remove it Immediately” is set, the message will not go to the Trash folder.
• If “Mark it as deleted” is set, deleted messages show a line through the text and a red “X” icon.

If you have a very large mail store, or if your server is older or slower or if you just like speed, you may opt to choose 'mark as deleted'.

• This is very fast and efficient as it simply changes an attribute of the message, rather than physically moving it.
• Messages will then display with a line through them showing them as deleted.
• Messages marked as deleted can be undeleted too.
• You can choose not to display messages marked as deleted so they don't 'clutter' the display.
• Messages are truly deleted with an 'expunge' operation
  • Messages marked as deleted are expunged when you Compact Folders.
  • You can also set Clean up (“Expunge”) Inbox on Exit
    • If set, messages get physically deleted when you exit from Thunderbird.

If you like to keep your deleted mail for a while and you have the disk space, you can use the (default) “Move it to the Trash Folder” option.

• This option uses more disk space.
• This option is slower by far than 'Mark as Deleted'.
• This may be more like what you were used to with other mail clients.
• You can specify the folder where deleted messages are stored.
  • If you use a 'local folder', deleted items will not be visible from other IMAP clients you might use such as webmail.
  • An IMAP folder is more universally visible, but uses up your disk quota if you have one.
  • You may need to coordinate (adjust) all of your IMAP clients to use the same Trash folder
    • Different IMAP mail clients default to using different folder names

Other folders that might need adjustments if you use more than one IMAP client might include:

• Sent Mail
• Drafts
• Templates
• Archives

Most users will make use of at least Sent and Drafts.

To adjust the folders into which these items are stored:

Tools → Account Settings → Copies & Folders

See also POP vs. IMAP or Why I Use IMAP

Being able to have all your mail clients display and use the same server-side IMAP folders is a wonderful thing, but one of the downsides is that every device/client does things a little differently. Some use the IMAP deleted flag, some use a “Trash” folder, others use “Deleted Items” (Outlook’s default). “Sent” is almost as bad: most clients use “Sent”, but many use “Sent Items” (Outlook’s default).

Mobile devices can usually be configured as POP or IMAP clients. If mobile devices are configured as POP accounts, you will not see Sent or Trash (deleted) items show up in your IMAP folders. If you want to see consolidated Sent and Trash items in your IMAP folders, use IMAP on all your other mail clients.

Webmail programs are virtually always IMAP clients and will see the same messages and folders as all other IMAP clients.

Mobile devices generally have fewer settings for Sent, Draft and Trash folder selections. For example, on one modern Android phone, you are not able to choose these folder settings at all.

Android default folder names for sent, draft and deleted items match the Thunderbird defaults:

Apple iOS devices like the iPad or iPhone appear to be more flexible, but their default settings may require tweaking for your needs:

To see Sent/Draft/Trash items in your IMAP folders, modify the settings to point to the corresponding folders on the server.

To modify the Sent/Draft/Trash folders on the iPhone:

1. Start at the home screen
2. Go to Settings
3. Choose “Mail, Contacts, Calendar”
4. Select an IMAP account
5. Scroll to the very bottom of the list, choose “Advanced”
6. Change each of the “Mailbox Behaviors” items as needed.