Every hourly Time Machine backup is quite large for me, but I don't change that many files so rapidly. I've determined that the main culprits are under ~/Library/Group Containers/UBF8T346G9.Office/Outlook/Outlook 15 Profiles/Main Profile. I'm hoping I can exclude something under here from Time Machine backups that will safely reduce the size of every hourly backup.

I believe MS Outlook 16.x downloads email messages and attachments from the Outlook server under here, just for indexing and speed reasons. If I ever had data loss, those email messages and attachments would be downloadable again from the Outlook server. Therefore, excluding these from hourly backups seems reasonable to me.

However, searching the internet for files to exclude from Time Machine backups never mentions this path. I can't tell whether that is because excluding these files is unsafe, or because MS Outlook 16.x is too new for people to have discovered these files. I find the latter hard to believe, especially since the path contains "Outlook 15".

Is there something under this path that I can safely exclude from my Time Machine backups?

  • Wow, nobody else on this site has or wants to know an answer to this?
    – Jim L.
    Aug 25, 2019 at 15:37
  • I wonder if excluding the mentioned folder reduced the TM snapshot and didn't cause problems in the long term.
    – Leonardo
    Jan 12, 2022 at 5:48

1 Answer 1


Don't have a real answer, just data to share. After losing a decade's worth of archived Outlook emails, to a drive failure, I tried restoring from TM. These were emails from previous jobs, to which I no longer had access, so my local cache was my record.

I had only mixed success - my user environment must have been corrupted by the drive failure, and even 1 year old backups would not get me my state back. Outlook kept wanting to "rebuild" my mailboxes, which required two or three times the original mbox size (~500G at the time of loss).

I didn't have terabytes worth of space for this, so I started picking and choosing what to restore. That's when I found that, indeed, the bulk of archived/cached local mail, lives in the ~/Library/Group Containers/UBF8T346G9* path.

But Outlook also has SQLite data files elsewhere, and perhaps other metadata too, and no combination of restores would yield a working Outlook state - i.e. no rebuilds, just my mailboxes/folders as they were.

So my conclusion is that although it's probably safe to exclude this path from TM backups, if things ever do go south, and you also lose access to the mail server, then you risk losing everything, with no way to restore.

Sounds like in your use case, that's probably not a concern.

Anyways, just one guy's Outlook & Time Machine story.

  • Sounds like backing up this folder is a complete waste, then.
    – Jim L.
    Apr 16, 2020 at 16:22

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