qmail-spp

Denying bad DNS HELO/EHLOs

The RFC-821 Section 3.5 states that  The sender-SMTP MUST ensure that the <domain> parameter in a HELO command is a valid principal host domain name for the client host. As a result, the receiver-SMTP will not have to perform MX resolution on...

Greylisting for qmail

Greylisting is a method of defending e-mail users against spam. A mail transfer agent (MTA) using greylisting will "temporarily reject" any email from a sender it does not recognize. If the mail is legitimate, the originating server will try again after...