Quote:
Originally Posted by xyzzy
Is there some reason you don't just set Spam learning for that folder to spam and possibly also Auto purge after a reasonable amount of time?
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Good question. I had my folders set up that way a few years ago. But Fastmail (in their help and in mypersonal email communication with staff) strongly recommends not setting the Spam folder for learning. This is due to the spam feedback learning loop which is created. For example:
- Let's say the Spam folder is set to learn messages as spam, with auto-purge set to 31 days. You might think that this would give you a full four weeks to get around to checking the Spam folder for false positives (ham treated as spam).
- Now let's say that your bank (or some other source) sends you two emails a day. In some cases the From address is not fixed, so you might not have it in you address book to whitelist. If one of those messages eventually exceeds the spam threshold (let's say one every six months), that message will be moved to the Spam folder and the folder settings will learn it as spam.
- Now emails from that same sender (or with similar spam indicators such as certain words or the sender reputation) will receive a higher spam score. So if the probability of a message from that sender was 0.1% one week, it might be 1% a couple of weeks later, and before long it's over 10%.
- You won't lose any ham (desirable) messages if you look at the Spam folder at least every 30 days. But more and more of the ham messages from that source will be missing from your Inbox, and since it's a somewhat random process it would be very aggravating!
- So how do you fix this problem? You could manually learn every false positive as not-spam, but that takes a lot of work! You could try to add a special rule to whitelist those emails, and that's also a pain. And now you need to look at the Spam folder several times a day to be sure you haven't missed an important message. This defeats the reason we use spam filters!
- This is much less of an issue for false negatives, which are spammy email which doesn't get caught by the spam filter and so get learned as not-spam. The spam messages which are learned in a feedback loop as not-spam will probably eventually change or go away when Fastmail starts blocking them at the SMTP stage.
- So it's best to not set the Spam folder to learn spam.
Bill