I have been using Spamsieve as a spam filtering drone on my server for a while and am very happy with it. Up until now, on the other computers, I have used two additional mailboxes in each mail account: TrainGood and TrainSpam. But to use this setup I have to check the account the spam was sent to and then scroll down in Mail to find that account before I can move the message to the TrainGood or TrainSpam mailbox in that account. I see in the manual that I can use a single pair of training mailboxes of one of my accounts. I don’t care what Junk mailbox the spam goes to. It will all end up in the trash anyway.
I would like to use the training mailboxes in the account that is the easiest to access in Mail, in my case it is, most of the time, my iCloud account. Can I leave the other training mailboxes where they are or should I delete them?
You can leave them. It doesn’t make a difference to SpamSieve if it’s checking empty mailboxes. You may find it helpful to keep these for training from an iOS device, since iOS Mail makes it easier to move messages within the same account.
The main disadvantage of using the “wrong” training mailboxes is that if there’s a false positive it will get moved back to the inbox in the account of the TrainGood mailbox, which may be different from the inbox that received it.
I see the potential problem, but it wouldn’t bother me if a message ended up in the wrong mailbox as I usually check “All inboxes” in “Favorites” in Mail. When I want to check to which account a mail was sent to I look at the “To:” item in the header.