SpamAssassin Rule: FH_FROMEML_NOTLD
Standard description: E-mail address doesn't have TLD (.com, etc.)
Explanation
The sender's address does not have a full Internet domain. The mail may have arrived from a misconfigured local machine that only used its local name (e.g. bilbo@hobbit), or else it is an attempt to disguise the real sender.
Further Info
The default scores for this rule can be found in the online list of tests.