Answer

PROBLEM

The Language Detection filter is not blocking short emails.

ENVIRONMENT

• GFI MailEssentials
• All supported environments

SOLUTION

There is minimum number of characters required for the Language Detection filter to work properly. The email body must have at least 50 characters, otherwise the filter cannot recognise the language, and the email will be skipped. This happens regardless of the email format (HTML/RTF/Plain text).
The behaviour can be verified from the debug log file ´..GFI\MailEssentials\Antispam\DebugLogs\ase_language_detection.gfi_log.txt´:

"ase_language_detection",">> Process Message"
"ase_language_detection","HTML body is invalid"
"ase_language_detection",">> CLanguageDetection::GetUnicodeText"
"ase_language_detection","Is this HTML [NO]"
"ase_language_detection","Charset [us-ascii] - Internet Encoding - [20127]"
"ase_language_detection","<< CLanguageDetection::GetUnicodeText"
"ase_language_detection","Plain text size is less then 50 characters...skipping detection"

CAUSE

The filter is working as designed and it is not considered as a bug. There must be minimum 50 characters in the email, otherwise the filter will not work properly.