Huge backup_client.db on mail server

My mail server VM ran out of disk space today. Short investigation lead me to discover the backup_client.db file was 7.5GB. On my other servers, it’s under 100MB.
The mail is stored in maildir format (so millions of small files)… Is this going to create a huge database? Should it be that big?

Is there a command to “compress” or otherwise reduce that size?

It stores the client-side hashes there. Are those enabled?

If that’s the default, then I assume so. Where would I check?
The local full and incremental file backup transfer modes are both set to hashed. Is that it?

So we’re not quite 2 months later, and this file has now grown to 14GB! There’s only 9GB of data on the entire rest of the the server.

Where should I be looking to disable the client side hashes? What impact will that have on the backup process?

Using separate setting, for that client only you can try 2 things
On internet, tab you can uncheck client hash.
In the advanced tab switch from hashed to raw transfert.

Just coming back to this again… It’s grown to 15GB since I deleted it in January. I had it set to raw for every setting in the advanced tab, but noticed I missed the client side hashes in the internet tab. Changed it now, but I have doubts it’ll do anything.

Still confused how the hashes for ~10GB of files can take 15GB to store. It’s emails, so lots of small files, but surely the hashes are still smaller than even the headers of the emails.

Similar issue here. backup_client.db is 38GB, larger than the actual amount of data that I back up. Just changed hash settings, but if that’s going to be the fix I think I’ll have to just switch products.