Why will Time Machine not restore Mail? I don't know how it happened -- I was reviewing my email on my old MacBook Pro, running Sierra, and somehow managed to send all of my Apple Mail Inbox emails to the Trash, and then they disappeared. Unfortunately, I did not back up the MBP. But, I have email being stored in the Cloud and am constantly backing up with Time Machine on my iMac, running Catalina. I am trying to restore Mail using Time Machine from the date before I noticed all of the emails were gone.
When I clicked Enter Time Machine, and selected the date I need to restore, Mail did not appear in the list of applications in the Finder. I went to the hard drive and found the Applications folder there, and found the Mail application, selected it, and clicked the Time Machine Restore button. This error message popped up:
“” can’t be modified or deleted because it’s required by macOS.
I checked the Trash and did not find the emails there.
Is there any way I can restore all my emails using another method?
Apple Discussions have not directly answered my question, given all the steps I have taken.
I have a new iMac running Catalina and I too found that I could not travel back in time when entering Time Machine from Mail (but it was OK when entering Time Machine from Finder).
The problem may be with backing up Mail messages.  During a Time Machine backup, the Console app issues unpromising messages including Couldn't create MailLibraryItem at path: /Volumes/com.apple.TimeMachine.localsnapshots/Backups.backupdb/(my mac)/2020-08-16-141340/Macintosh HD - Data/Users/(my user)/Library/Mail/V7
I have just spoken to Apple support, and their engineers are aware of the problem and are working on a fix, to be included in a future OS update, which is great news.
I appreciate that this reply doesn't help with the original problem, but the lady from Apple I spoke to did say that there may be other ways to restore lost email messages, so it might be worth your while calling Apple support.  Good luck!