Spam Filter "Leaks" Sometimes

I have recently set up a Virtualmin + Ubuntu 12.04 server for a small professional operation with a relatively light loading of web access and email traffic.

Spam processing is set up so that identified spam goes is sent to a specific spam folder. However just once in a while small bursts of spam (typically 3 - 5 items) arrive in the in the primary inbox rather than the spam folder, even though positively marked with a high score as being spam.

Email on the server is otherwise working well and mostly giving a good degree of protection from spam thanks to standard Greymail and SpamAssassin setup. The only characteristic of the mis-directed spam that I can see is that the spam items have arrived within a few seconds of each other.

Any suggestions appreciated that might help me to clear up this issue.


Users have WebMail access?
Maybe some of your users made some custom rules for incoming email?

Thanks for the suggestion, but I’m the only site user.

One of the things I noticed is that it was only affecting the domain where I had used the “Write to mail file under home directory” option to direct spam to a folder other than the default (~/Maildir/.spam/). So maybe something related to this post:

Also noticed that the default spam mailbox domain was not stable and had changed to ~/Maildir/.Junk/ without me being aware that I had done anything to cause that.

I think its fixed now. I found the built-in script to set the spam folder destination across all servers, and applied it using the folder to my choice. Now all spam is reliably going into that folder.