Mail loses signatures

Hello everyone.

I have had this issue for a few years now, but yesterday needed to make it work, so I found a lot of topics about this problem on the internet; it is evident that this issue affects many people and despite that, there's still no fix from Apple. So I tried to figure it out.

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I located the directory where the signatures are stored in the system library. Three files are basically needed to assemble the single signature. The first file is .mailsignature (the file with your actual signature [you can have multiple of these .mailsignature files — one for each signature]), and the other two types are .plist files (one where you can find information about your signatures associated with accounts, and the other for listing of all your signatures). 

I found that when you create a new signature it is successfully written into a file called AccountsMap.plist, but there are no .mailsignature files created and that's probably the reason why it is not written into another .plist file (AllSignatures.plist). You can not write and create these files manually (at least, it didn't work for me). So I tried to turn off iCloud for Mail to see what is happening inside the library and it started to work perfectly and create all files you need to work with signatures. So it seems to me there is some problem with syncing into iCloud. 

(Don't try renaming or deleting any library files if you don't know what you’re doing, it can have fatal consequences (and if you do, always back up the original files).

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The solution.

All you need to do is temporarily turn off iCloud for Mail, then create signatures and turn the iCloud for Mail on again, so it's an easy fix (unless Apple fixes it properly). To do this, follow the steps below:

1. Quit the Mail app.
2. Turn off iCloud for Mail (go to System Settings —> (your name) —> iCloud —> iCloud Drive —> Options —> (uncheck the Mail).
3. Launch the Mail app.
4. Create signatures as you want them, assign them to accounts, etc.
5. Quit Mail
6. Turn on iCloud for Mail (go to System Settings —> (your name) —> iCloud —> iCloud Drive —> Options —> (check the Mail).
7. Launch the Mail app; all your signatures should be there.

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Note 1:

You need to repeat this process every time you'd like to make changes or add a new signature. 

Note 2:

Signatures are still not synced over other devices (I am not sure if it's a bug or expected behavior and it is not supposed to be synced across all devices).

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I hope this helps.