Under Big Sur my Mail Trash folder is missing from my favorites. How do I get it back?

Scroll down the side bar to the bottom where the Inbox, Sent, Junk, Trash and Archive mailboxes for each user account your have and drag the Trash mailbox up to the Favorites section.

Or you can create a smart album with this criteria:

and place it at the top of the Smart Mailboxes section:

This is much easier than most of the replies indicate. I had the same issue after upgrading to Big Sur. Simply open your email, in the left sidebar, at the very top above "All Inboxes" you will see "Favorites". Hover over "favorites" and then click on the + sign. A box will open. Click on the arrow in the drop down menu and choose the folders you wish to display. If you have more than one email account, click on "All Trash". That will add the trash folder back and all your deleted emails will be there.

Boot into Safe Mode by booting with the Shift key held down and try from there.  Reboot normally and test again.

NOTE: Safe Mode boot can take up to 10 minutes as it's doing the following; 

• Verifies your startup disk and attempts to repair directory issues, if needed

• Loads only required kernel extensions (prevents 3rd party kernel/extensions from loading)

• Prevents Startup Items and Login Items from opening automatically

• Disables user-installed fonts 

• Deletes font caches, kernel cache, and other system cache files

Ever macOS seems to change this approach a little bit, try this one—

To see hidden directories/ .files using the 3 key combination: Shift Command . (period)

From your home folder grab the .Trash directory and drag it to the side bar.

Report back your success or failure.

Try the way I first did: scroll down to the bottom of the sidebar where you see the various mailboxes for your email accounts

Click on the Trash bin you want and drag to the top and place after the Drafts mailbox.

I added the trash folder back to Favorites successfully (as an aside... I think some folks are struggling finding the "+" symbol because you have to contract the grey sidebar temporarily to make the "+" situated right next to the word "Favorites" -- when it's a little over to the right, it keeps disappearing).

However I have multiple email accounts, and every time I delete something it keeps creating a new "trash" folder for that particular email account under "On My Mac". I have around 10 email accounts, and will eventually end up with 10 extra trash folders under "On My Mac". Anything I delete goes to the "favorites" trash folder (which is acting like a smart mailbox without me setting it up this way) but the individual trash folders under on my mac... can't figure out why there are there, or how to stop that. Any suggestions?

In the "mailbox Behaviours" for each email account I have each set to

Trash Mailbox > On My Mac > All Trash

Same here. I typed "trash" in the search bar and chose the proper account trash and the mail crashes. Then I deleted a message, searched for that message and can view it that way, but still no folder?

Isn't that the truth, I seem to learn every day also. That's what's so great about these communities, we all learn from each other. I'm sure that I learn a lot more from you and others than I can offer in return. I'm glad it helped.

Tried the idea of hovering above Favorites. But in my case, nothing happens (unlike hovering over any of the other section heads) - there is no + that appears. Could this be related to a setting I may have missed?

No. I don't get the + when I hover over Favorites. I do get the Plus when I hover over other headings ... iCloud, My Mac, etc. Strange. I have multiple mail accounts and am trying to get back to an All Trash Mailbox, so that I can manage all trash in one go.

Yup, that works. But (given that I have 3 different mailboxes), I end up with 3 different trash mailboxes in favorites ... instead of everything together in a single, consolidated 'All Trash'. Not the end of the world ... but not ideal either. Thanks so much for the suggestions.

Thankfully the answer is here.

Why does Apple have to screw things up all the time with stuff like this? If it ain't broke, don't fix it. I hate this stupidity, what was wrong with the previous OS having Junk and Trash folders? Do they expect us to delete things without the opportunity to see what we are deleting?

Hi. Thanks for all the helpful info. After doing the above, my deleted mail was still not syncing to the iCloud All Trash folder. I have four non-apple email accounts ... and the other three all had a 'Trash' folder that synced to the respective 'All Trash' folder. However, after updating to Big Sur in my iCloud account a new folder named 'Deleted Items' appeared instead of a 'Trash' folder. I solved the email syncing to the correct icloud 'All Trash' folder by taking the following steps ... >Mail >Preferences >Accounts >iCloud IMAP >Trash Mailbox >Click and choose 'Deleted Items' folder. Now all my deleted mail shows (as it does in 'Trash' on other Apple devices). Hope this is helpful.

I updated against my better judgement to Big Sur. Now I can't access my trash with either gmail or hotmail. I moved the trash folders up to my favourites but they were and remain empty. Where are my deleted messages going and how do I access them??

The easiest way is to just click the "+" next to Favourites, and then re-enable Trash (as well as Junk, Archive, etc..)