Does spam ever get filtered silently?

I’m noticing that some emails I’m expecting to come through are not in inbox or junk. If an email is caught in any of the spam tools, will that always result in them being put in the junk folder, or, are there ever cases where emails are blocked further upstream and don’t even get placed in junk?

These are newsletter subscriptions, so, I can’t be 100% sure that the problem isn’t on the sender’s end. However, knowing this piece of information would help me diagnose.

If it is the case that emails can fail silently, would there at least be evidence of the delivery attempt in the log files?

I am definitely no mail expert, but as far as I know, everything from the outside world going into your mail server goes to your MTA (mail transfer agent) FIRST. Your MTA then decides what to do with the mail, whether that is to throw it at a MUA (mail user agent) or your filters, I forget what the MTA does after it gets mail.

Now, I do believe that your MTA, Postfix does keep logs of certain things, such as the IP addresses, time and maybe a couple of things, regardless if it is spam or even if there is a mailbox or not for the user it is being sent to.

I would definitely check out your Postfix log.

Take a look in Postfix logs, look for 550 in the messages. Spam Assassin usually pushes to Junk but certain messages can be blocked dropped by Postfix if it is configured to do so even before it passes them off or even accepting the full message.

Details of how Postfix directly handles Spam or UCE as Wietse Venema calls it can be found here:

Check the configuration of Postfix using the postconf command to see if anything is set to reject outright. The man page is a bit daunting but this should give you all you need.

Yeah, so I believe Postfix mostly rejects mail if the sender is badly configured. For example, if someone is trying to send you mail from a server that is not the domain they claim they are in the message, I believe Postfix will throw it in the abyss.

However, if your mail is being transported correctly (or acceptable by your Postfix’s configured standards), then it is probably spamassassin, blacklist, or other filter. Obviously, if you’re sending mail from a blacklisted server, it’s going to fail.

If it’s neither a transport issue or a blacklist issue, it probably is Spamassassin detecting the message body as spam, or unwanted by the context or how the email was worded. If the email says something about Russian girls wanting to… then Spamassassin will probably think it is junk. If it is really confident a piece of mail is junk, it won’t even make it to the junk folder. But if you’re getting an email from Google for resetting your password (and it passes through transport security measures from Postfix), Spamassassin probably will think it’s not spam (or a really low spam score). If your friend from 10 years ago emails you asking for money, chances are, Spamassassin will give it a medium spam score and allow it to make it to the junk folder.

So if it makes it through transport, it’s all about the spam score. Really high spam scores don’t even make it to the junk folder. Medium spam scores make it to the junk folder, and lower spam scores make it to your inbox. Spamassassin is always learning too, so it will figure out what you call spam and not.