Because I consider backing up mail as important, I added c:\Users\UserName\AppData\Roaming\Thunderbird\ to my folders to backup; that's where Thunderbird stores all profile data.

However, since then I get irregular conflicts between the programs when Thunderbird does its 10-minute mail fetch:
"Unable to write the email to the mailbox. Make sure the file system allows you write privileges and you have enough disk space to copy the mailbox"

It looks like when Thunderbird is updating the (quite large) files containing the mails, it gets into conflict with CloudBerry that has detected a changed file and wants to back it up. The same sometimes happens after sending a file when it need to be copied to the 'Sent items' folder.
I have the same issue e.g. when I download a file, then move it to another disk: the delete after the copy fails, but works again if I wait a few minutes and then manually delete the file.

That last example does not bother me much, but the email issue is becoming a nuisance - especially since email is much more critical.

Is there anything I can do to prevent this (other than setting lower frequencies) - a setting I may have overlooked perhaps?

- The backup job is scheduled to run every 4 hours. The backup is to Amazon Glacier. Typical backup duration is 1-2 hours, for 1000+ files, approx 1 GB.
- Thunderbird updates its mail every 10 minutes.
- CBBackup is at version 5.8.6.27 (I just notice that 5.9.2.30 is available but don't expect that to change much).