I am sending email messages from a PHP script to an Exim 4.71 server via SMTP. The server advertises pipelining so I am trying to take advantage of it. However, when I read back the return codes I finally get
554 SMTP synchronization error. On the server side the error reads:
SMTP protocol synchronization error (next input sent too soon: pipelining was advertised): rejected "DATA" H=(localhost) [126.96.36.199] next input="To: email@example.com\nDate: Wed, 12 Jun 2013 11:35:50 +1200\nReturn-Path: firstname.lastname@example.org\nSubject: Blablablablabla"
I am wondering why is it saying "next input sent too soon". I am using pipelining and so should be allowed to send my data not waiting for anything.
Note that when I do not use pipelining it all goes fine.