On Wed, Aug 14, 2013 at 03:23:11AM -0700, Grant wrote:
> A few people have told me they received an email error message 
> after emailing me.  I'm trying to get a copy of one of the error 
> emails, but I can't imagine what would cause that besides possibly 
> my greylisting.  Has greylisting been known to lead to email error 
> messages being sent to senders in some instances?

In Postfix, see delay_warning_time: "To enable this feature, specify 
a non-zero time value (an integral value plus an optional one-letter 
suffix that specifies the time unit)."

delay_warning_time is disabled by default, but might cause the 
confusion you are describing. Sendmail and other MTAs have similar 
features. I think Sendmail's might be enabled by default at 4 hours.

http://www.postfix.org/postconf.5.html#delay_warning_time

It's not unheard of for greylisting to cause delays in excess of 4 
hours, especially for senders from large providers like Gmail. Gmail 
hands off deferred mail to an outbound farm which always tries from 
different IP addresses, thus meaning more delay with each unknown IP 
address.

> How is greylisting set up in postfix now?

I won't repeat the other replies you got about policy services, but 
I'll mention that postscreen(8) can provide most of the pain and 
benefits of greylisting, by enabling the after-220 ("deep protocol") 
tests.

http://www.postfix.org/POSTSCREEN_README.html
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