This question arose on an unrelated BB.
Can Moderators/Admin read PMs between other people? 

I'd say not really easily but if admins/moderators are able to make back ups of the database, then technically (with the right know how) they could look at the backup file.
I doubt basic moderators would have that access...

Remembering that a backup is only a snapshot of that moment so if you read and delete then I'd imagine that would keep you safe from prying eyes...

I would think it would depend on how the board is set up and also what permissions are allocated to board Admin/Mods. Personally I know that I deliberately send some PM's on another BB as I am sure that someone would be sad enough to be monitoring certain folks chat and would have the know how to possibly even extract certain messages as they are sent to view them later, but maybe I am just paranoid 

Cya
E
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