Time Machine Does Not Restore Emails - Don't Think you have Backup!

To retain email messages Time Machine will back up along with everything else, create a local Mailbox, i.e. one on your Mac.

Excerpted from Create or delete mailboxes in Mail on Mac:

• On My Mac: Mailboxes you create in On My Mac are local, meaning you can access them only on this computer.
• Account: Mailboxes created on your email account’s mail server can be accessed on any computer or device where you use the account.

If you delete the latter—not On My Mac—they are deleted from your email service provider's mail server. They're gone. Time Machine does not back up Mailboxes stored on your email service provider's mail server.

It is the way it has worked until now. If it weren't intended to work this way there would be no mail interface in the Time Machine window. We used to be able to restore individual emails from the TM Mail interface because I have done it many times. The same used to hold true for photos. For example, in years past we used to be able to restore individual photos from the Time Machine iPhotos interface. Apple removed that functionality and removed the interface. When you launch TM from the Photos window now you are presented with the Finder interface. So just want to clear up that we are not imagining this change in Time Machine Mail recovery functionality.

As far as the TM not storing emails from the server, that is not how it had worked before. Mail accounts set up with IMAP are in sync. When something happens to the mail on the local system it is also reflected on the server and vice versa. Mail does store mail locally even for IMAP connections. If it did not, you would not be able to see the emails (that you have already received) after disconnecting from the internet. So again, Apple would have had to change the function in order for TM to no longer backup mail that is indeed stored somewhere locally.

Apple may choose to handle iCloud mail in TM differently than mail from other servers, but TM does not display -or displays only partially- any mail from any account in my Mail app.

If Apple is not phasing out support for a Mail interface in TM, then I wonder if the TM app is looking at the local TM backup and stopping there without reaching out to the TM backup file on the external drive. ? a possibility.

I understand. I surmise that you're expecting TM to be able to restore deleted email messages and that's just not the way it works. On the other hand if you suffer from a catastrophic disk failure TM will absolutely, positively restore emails that you did not delete, regardless of whether you stored them "on my Mac" or left them on the email server.

The same concept applies broadly to TM in general: if you delete a file from your Mac, it will also be deleted from its backup—with the additional caveat that it is only deleted after a period of time.

Keep in mind that TM is not an archival system and was never intended to be one. Retaining emails for archival purposes requires either not deleting them from the server or storing them locally "On My Mac". In both cases, TM absolutely, positively, backs them up.

I've erased and restored many Macs in that manner many times. In fact I have a local Mailbox titled "keep forever" which contains messages predating the age of this Mac by fifteen years.