strict interpretation of rfc (2)821 for mail from an rcpt to commands

RFC (2)821 doesn't allow a space between the colon and the mail address in the MAIL FROM:<> and RCPT TO:<> commands. Lots of spamware and worms insert a space, but the well-known MTAs (sendmail, qmail, postfix, MS-Exchange) don't.

So a strict check of the syntax can block quite a lot of mail and worms. According to Claus Assmann, sendmail X will check the syntax strictly. I have modified qpsmtpd to do this (but also implemented a whitelisting feature to allow for broken MTAs).

Here are some results:

Broken MTAs

A list of probably legitimate MTAs which include spurious spaces in MAIL and RCPT commands:

IP-Address SMTP banner Software 220 **************************************************************0*************************200***0****0***0*00 Unknown - masked by a PIX firewall 220 - MAILSCAN1 eSafe SMTP Service 4.2.533.2 ready 16-Feb-2005 10:35:34 Aladdin eSafe 220 Service ready by DvISE PostMan (0224) ESMTP Server (Tobit Software, Germany) Tobit DvISE 220 ESMTP MailEnable Service, Version: 1.71-- ready at 02/21/05 14:55:23 ??? 220 ** Unknown - masked by a PIX firewall