Train spam filter
PIL uses a dynamic spam filter to sort mails which are/can be spam. This filter is of course not 100% flawless, in the sense that it can sometimes see a legitimate mail as spam because it contains some factors spam mails also do. This is a 'false positive'.
To 'train' the spam filter, you just have to move a mail from your inbox into the spam folder, this goes both ways, that means if you notice a legitimate mail in the spam folder, it's just moved from the spam folder to the inbox. This 'training' can be done in your email client (outlook/Thunderbird/Apple Mail etc.) or via the PIL webmail.
The spam filter is individual, so that when you 'train' the spam filter, it only applies to the account you're logged into.
Furthermore you can also change how 'hard' or 'soft' the spam filter is. This is done by logging onto webmail.pil.dk and clicking on the cogwheel.
Then click on 'Filters' and 'Spam (Move to "Spam")'.
The amount of asterisks specifies how 'hard' or 'soft' the spam filter is. So if you for example experience that a lot of emails end in the spam folder, you can adjust it by deleting a star and seeing if it improves. If it doesn't improve, remove another asterisk and so on. When you've chosen the amount of asterisks, click "Done" to save the change.
As a note, you can create your own filters in the 'Filters' menu.