SpamAssassin, a tool that is widely used as open-source anti spam detection system, had an issue on Janaury 1, 2010 with a rule that compares the date of an email message to detect emails from the future which could be an indicator of spam.

For the readers that are not familiar with SpamAssassin here is a brief explanation on how SpamAssassin works. SpamAssassin will check each incoming message and will check the message based on rules. These rules contains information on what to search for and defines a score when a similarity is found.

The rule FH_DATE_PAST_20XX checks if a message is sent in the near future and will increase the score  with 3.2 points if this is true. Apparently, the search date was 01-01-2010.

This caused that all messages had an increased score by 3.2 by default. Combined with other rules, the score per message can increase further and eventually the message can be labeled as spam by SpamAssassin, depending on the configuration, that leads to many false positives.

The date for the rule has been changed to 01-01-2020 according to the SpamAssassin Wiki.

More information:

Mike Cardwell Blog
IT Slashdot

I do hope that the SpamAssassin admins change the rule on time to avoid a 2020 bug in their rule set.

In case you’re wondering…. no, MX Lab does not use SpamAssassin so our services were not affected by this issue.