Question about Outlook Express

I use Outlook for Mac 2011 on a MacBook Pro. The backup method has been to use CrashPlan, a highly regarded commercial service that automatically backs up all files to a local server or to CrashPlan's own storage via Internet. Recently the laptop was lost. I initiated a restore of all laptop files to a new laptop, and all files restored successfully -- except for Outlook's.

Here's what happened during recovery. I installed Outlook on the new laptop, deleted the files in /Users/username/Documents/Microsoft User Data/Office 2011 Identities/ that were set up by default, and copied the restored contents from the restore location to that location. I then started Outlook, and received the message that the database needed to be rebuilt. After the rebuild, Outlook started but large amounts of email was missing. Some very recent email was present, but the bulk was not present. There seems to have been data corruption as well; some email dates were set to year 2018, and there were many recovered folders. So, having lost years of email, I now ask how I should backup Outlook for Mac in the future.

I ask because on PCs, the Outlook 2010 mail file (a .pst file) will not back up automatically if Outlook is running, as the file is locked against another open attempt. One has to shut off Outlook 2010 to get a backup. But I read that, on a Mac, Time Machine will back up all files, and I see no mention of shutting off Outlook.

Assuming that CrashPlan backs up all files it can, what do you think went wrong?

Am I correct in assuming that Outlook for Mac cannot be reliably backed up by automatic means? In that case, my strategy is to use File | Export and save the .olm file manually to a location that CrashPlan backs up every time it is saved.

Thanks for help.