I had the suggestion earlier that it could be pipelining related, and saw a similar thread but...
Assuming that is the problem then that error message really doesn't make sense since Pipelining is an RFC 2821 (and related) compliant feature.
Further, I don't feel I should have to disable a legitimate SMTP feature just to get along with GMail. Especially since it would actually be GMail that would be the one violating the RFC (unless there is an as yet unreported Postfix bug which is highly unlikely).
And finally, even though the thread reports that after disabling pipelining (I assume that is what that postfix option effectively does) things started working. However, I did nothing and things started working so my guess is that the fix is required.
The error hasn't happened again since at least Nov 9th (last time the log was rotated) and all the mail did finally get through though it was much delayed.
My gut feeling is that it is some kind of GMail spam reduction related to pipelining but after you persist enough GMail "learns" that you are not an "evil pipeliner" but are using that feature legitimately and starts letting mail through on the first try.
- John Lange www.johnlange.ca
On Wed, 2008-11-12 at 17:53 -0600, Sean Walberg wrote:
On Wed, Nov 12, 2008 at 5:16 PM, Gilbert E. Detillieux gedetil@cs.umanitoba.ca wrote:
> 451 4.5.0 SMTP protocol violation see RFC 2821 Usually, an error message like that would suggest something is messed up in the MTA configuration at one end or the other. Did you bother to check this site for likely possibilities?... http://www.rfc-ignorant.org/rfcs/rfc2821.phpWhich one of the 79 pages do you suggest he starts with, Gilbert?
While you're mulling that over, I'll suggest something more helpful:
http://forums.devshed.com/mail-server-help-111/gmail-responds-451-4-5-0-smtp...
Google's the one at fault here, the thread has a workaround from the postfix mailing list, and seems to have fixed the problem permanently.
Sean
-- Sean Walberg sean@ertw.com http://ertw.com/