Nikolaos Milas:
> Hello,
>
> We are running 2.9.4 on CentOS 6.5 as a mail gateway.
>
> A mail admin of a cooperating entity has reported that their sender
> checking to our org produces a protocol error and after that their
> system marks our mail as junk.
>
> Here is a session they provided (I only changed the mail adress username
> with "existing_user"):
>
> 220-mailgw1.noa.gr ESMTP NOA Mail Srv XAPITI XPICTOY
> HELO lala
> 250 mailgw1.noa.gr
> MAIL From:<>
> 250 2.1.0 Ok
> RCPT To:<existing_u...@noa.gr>
> 550 5.5.1 Protocol error
They have a buggy SMTP client.
The client is PIPELINING the SMTP commands, but Postfix has not
announced support for SMTP command PIPELINING.
I recall that some "antispam" software did this.
You can whitelist them with postscreen.
Wietse
