Support for failure-over destination SMTP servers. Many New DNS lookup functions. ORBS support has been disabled. This filter detects this trick, and rejects mail that has exploited Sendmail in this way. Since the vast majority of email from dialup accounts is sent through an ISP's mail server, and spam is routinely sent directly from a dialup account, the DUL is effective in blocking spam directly-sent from a dialup account.
Spammers sometimes use a blank MAIL FROM to hide their tracks.
This filter detects this text, and rejects mail that contains it. One of the disadvantages of using a relay server, such as MailShield, is that MailShield does not know if all the recipient accounts are all valid until it actually sends the final message. Performance is further improved by an in-memory caching of valid recipients. This feature allows you to do that. Feature to limit length of MIME attachment filenames, blocks well known exploit Some email clients crash when they receive email with a very long filename in an attachment.