Check Why Email Failed SpamAssassin Check

I use a private Mail-in-a-Box email server for hosting my own emails, which I like as it gives me full control. Unfortunately, whenever I received emails from one particular organization, the emails would always go to spam and I could not figure out why, until now.

Steps

Apache SpamAssassin (which is setup by default with mail-in-a-box), will put details of why an email fails a spam check, in the headers of the email. Thus if you are using a web mail provider such as roundcube (another mail-in-a-box default), then one can just click the headers link above the message as shown below:

A modal will pop up with all of the headers. You will probably want to make it larger by dragging the bottom-right corner.

In this modal, we can see the SpamAssassin score (1) and what is the threshold for failing the check.

The breakdown of how the score was calculated can be seen in section (2), which shows how all the little things can increase or decrease the spam score. In this case, we can clearly see that the biggest issue is that the email failed the SPF check (3), so the DNS SPF record needs to be fixed.

URL Grey List

Also of a minor note is the fact that one of the URLs in the email appears to be on a "grey list", with this showing up in the headers:

1.1 URIBL_GREY Contains an URL listed in the URIBL greylist

You can read about their various lists and what they are for on the website under "List Information".

Luckily, one can easily check ones own URLs against this list before sending out emails, if one needs to.