Why does a digitally signed message become invalid when scanned by GFI MailEssentials?

Answer

If a message carrying a digital signature is modified when scanned by GFI MailEssentials, the signature and the checksum becomes invalid in the following instances:

• A disclaimer is added when an outgoing digitally signed email is scanned by GFI MailEssentials.
• Part of a digitally signed message is quarantined by GFI MailEssentials and replaced by the notification text.
• The email is quarantined and approved by GFI MailEssentials.
• An HTML mail is sanitized by the HTML threat engine.
• The subject of the email is altered by the anti spam module to reflect the original recipient and the reason for blocking.
• The email is sent to a newsletter or discussion list that is configured in GFI MailEssentials.
• GFI MailEssentials add automatically a X-Header to every email which is identified as spam. 

To avoid such situations you can disable the X-Header feature by performing the following steps:

1. Open registry editor (regedit.exe)
2. Browse to the GFI MailEssentials registry node, which are:
   • x86: HKEY_LOCAL_MACHINE\SOFTWARE\GFI\MailEssentials\Antispam
   • x64: HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\GFI\MailEssentials\Antispam
3. In the sub node named 'Config', set the value of 'addmaspamxheader' from '1' to '0'
4. Restart the following service:
   • x86 - IIS Admin
   • x64 - GFI MailEssentials Scan Engine

Notes:

• This x-header is placed in the email when the email is detected as spam, not when it is whitelisted.
• This x-header is inserted in the email so that if GFI Archiver is also installed on the same Microsoft Exchange server, it would identify spam emails and exclude them from archiving.