It seems we are running into an increased number of hosts that have
broken smtp pipelining. We are able to resolve delivery issues to these
hosts using the solution that Wieste recommended a couple weeks ago:
http://www.mail-archive.com/postfix-users@postfix.org/msg44135.html
However, I'm not sure I fully understand why this fixes the problem for
outbound email. On outbound email, Postfix is acting as the client and
therefore one might think that smtpd_discard_ehlo_keyword_address_maps
would not have any affect, since this setting is supposed to suppress
EHLO keywords in response to a client. Does
smtpd_discard_ehlo_keyword_address_maps also ignore EHLO keyword
responses it receives on outbound connections?
I'm guessing so, because unless something else changed, the solution
worked. In fact, the above mentioned thread that Wieste is responding
to was also an outbound delivery issue, and so it seems he might be
implying that smtpd_discard_ehlo_keyword_address_maps has an effect on
outbound connections as well.
Ok, so assuming this solution works for outbound connections, this
solution would require that we create and maintain a list of perhaps
thousands of servers that have this problem. Does anyone have any
experience with just turning it off completely for all hosts? Which, I
suppose would be done like this:
smtpd_discard_ehlo_keywords = pipelining,silent-discard
Aside from a little extra bandwidth, would this cause outbound
deliveries to go horrendously slower on a busy mail server?
And is there a way to only disable smtp pipelining for outbound
connections only?
I better stop asking questions now since I might be getting ahead of my
self if my assumption about smtpd_discard_ehlo_keyword_address_maps does
not actually apply to outbound email...
Thanks,
Curtis
