Postfix long delivery delay when sending 5000+ mails

Paul Graydon paul at
Wed Apr 13 18:40:16 UTC 2011

On 04/12/2011 08:27 PM, Nicolas Barcet wrote:
> On 04/13/2011 03:33 AM, Lox wrote:
>> Hello,
>> I face a problem on my shared hosting server. I have a user that
>> regularly sends some newsletters to about 5000 recipients. When this
>> happens, it prevents other user from sending and receiving message for
>> more than 12 hours.
>> There are many options in postfix so I am not sure which one to tune up
>> to prevent such an issue, can anyone advices me on that ?
>> Any advices on my postfix (attached) configuration is also greatly
>> appreciated...
> My solution for this is to have a different postfix server handling the
> distribution of mailing lists and newsletters than the one handling my
> regular emails.  Mailing list even have their own subdomains
> "" so that the mx is handling emails (and bounces)
> separately from others.
> Nick
I've done similar here.  Plus on the mailing list server I've got some 
strict rate limiting taking place to try to reduce the likelihood of 
being blacklisted.
Blacklisting should be of serious concern here.  If you're throwing out 
thousands of e-mails as fast as the server can manage, the odds of some 
service blacklisting the box increase.

We use the following to restrict concurrency and rate:

default_destination_concurrency_limit = 2
default_destination_recipient_limit = 5
default_destination_rate_delay = 60s

that puts the maximum possible rate as 300 per domain, per hour, with a 
minute delay between attempts to send to a specific domain.


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