What does a backup do?
How do you normally use a backup?
Either you do a full restore or a partial restore. For the partial restore you usually notice „oh, I deleted the file or the folder some days ago“. You locate the folder in the backup. Then you try to merge the folder with the data on your hard disk.
All steps can’t be done in regards to email.
Which emails are missing?
Like everyone else you get of lot of emails. Can you say with 100% certainty which emails you are missing?
When did the emails go missing?
You can’t even say when the emails went missing. Perhaps your deleted some emails accidentally last week and Mail deleted some emails the week before. And if you don’t know when the emails went missing you don’t have a good chance to find them in the backup.
How to locate the missing Emails?
Backups keep the current data but not all historical data. If you notice today that emails went missing 4 weeks ago your backup may or may not have the data.
And how do you find the missing emails in your thousands of thousands of emails? They don’t have a good name. Instead there is just a number. You can’t do a search. You can only guess.
The restore doesn’t help either
Let’s say that you can identify that some mails went missing and you found them in a folder in the backup. That doesn’t really help you.
No email client has the concept of a duplicate email. They all happily keep multiple copies of emails. If you do a restore of a folder you now have a total mess of duplicate emails in your email client.
So how does Mail Archiver help?
With Mail Archiver you can at least find your emails again if periodically archive them. Mail Archiver fishes out the duplicates automatically. And if necessary you can do a partial restore via IMAP. But even there the lack of duplicate handling in mail clients is a problem.