On 11/10/2015 6:29 AM, Zalezny Niezalezny wrote: > Dear Colleagues, > > I would like to understand how Postfix receiving message. I expect > that Postfix has been written base on the RFC rules so maybe > somebody will be able to explain me how its working inside - how > this system receiving message and what is going on in the background. > > Our consultant hardly trying to tell us that server during receiving > phase checking MX record of the domain from which coming the E-mail. > Does it really working this way ? I always thought that Postfix > checking first DNS A record (reverse dns), then SPF etc.etc. > > I always thought that MX record is provide clear information about > the servers to which client needs to send a message. But right now > I`m completly out of space... > > > Does system check mx record when its receiving message or not ? > > > Do You know where may I find RFC which fully describing this SMTP > process ? > > > > With kind regards > > Zalezny > > >
RFC5321 describes the mechanics of SMTP. There is no requirement for the receiver to lookup the MX of the sender domain, but it might be done as part of anti-spam controls. Postfix MAY lookup the MX of the sender if you've configured anti-spam controls such as reject_unknown_sender_domain or add-on software such as an SPF checker. In particular, there is no requirement that the MX of the sender's domain match the sending client IP, and they often don't match. -- Noel Jones
