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I routinely run the Outlook PST repair tool (scanpst.exe) on my .pst file every few month. I like to make sure that my mails are not becoming corrupted slowly over time.

I never noticed any data loss. Outlook never reported any errors to me. Yet, the tool spits out very many errors on every check I perform. Here's a sample of the 2MB log file the tool generated:

**Attempting to validate AMap
...
!!AMap page <@17408> has csFree of 54, but should have 62
!!AMap page <@525312> has csFree of 135, but should have 177
...
??BBT entry (EBF8E5C) has different refcount in RBT (4 vs 3)
??BBT entry (EBFA99C) has different refcount in RBT (4 vs 3)
...
??Couldn't find BBT entry in the RBT (2BD4F74C)
??Couldn't find BBT entry in the RBT (2BD4F750)
...
  !!Folder invalid high-water-mark (nidi=A8018, nidiHigh=C281B)
...
  !!Search folder invalid high-water-mark (nidi=A798D, nidiHigh=BDE8F)
...
  !!Contents Table for 8082, row doesn't match sub-object:
    irow = 30641, RowID = 2BE37C4

Just tons of these worrying messages. My disk is fine. Nothing else is ever becoming corrupted on this machine.

Do I have to worry? What's causing these error messages?

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These problems still exist in O365 Outlook 2019. The scanpst.exe tool has been updated but it still can't fix all problems. If your PST is a static archive I see no reason to regularly repair it. You could even mark it read-only. Contrary to your intention, running a repair when it's not needed could introduce problems.

Try to keep your PSTs small, less than 2GB, as The larger the file is the more likely Outlook is to make a mistake. It's always been this way. Microsoft has made improvements but they've never made Outlook bulletproof. Also, if you keep your archives broken in to 2GB chunks then if one goes bad you don't lose everything, just that chunk.

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    Typically the point of an .PST file is that the emails no longer exist on the server and are used to archive the emails. So your suggestion of "making a backup" and then deleting the .PST file (which is the backup) is confusing. – Ramhound Jan 3 '19 at 18:40
  • It's not just confusing, this answer is actually dangerously misleading because it conflates PST files with OST files. While a deleted OST file will be recreated the next time Outlook opens, a deleted PST file will not and is gone. @HackSlash I suggest you read this: contactgenie.info/… If anyone reading this deletes their PST files in the hope that they will magically reappear, they'll be in for a bit of a shock! – Mr Ethernet Dec 15 '19 at 4:16

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