Может это подойдет
http://www.postfix.org/QSHAPE_README.html
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When a destination is unable to handle the load even after the Postfix process limit is reduced to 1, a desperate measure is to insert brief delays between delivery attempts.
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In the transport map entry for the problem destination, specify a dead host as the primary nexthop.
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In the master.cf entry for the transport specify the problem destination as the fallback_relay and specify a small smtp_connect_timeout value.
/etc/postfix/transport:
problem.example.com slow:[dead.host]
/etc/postfix/master.cf:
# service type private unpriv chroot wakeup maxproc command
slow unix - - n - 1 smtp
-o fallback_relay=problem.example.com
-o smtp_connect_timeout=1
This solution forces the Postfix smtp(8) client to wait for $smtp_connect_timeout seconds between deliveries. The solution depends on Postfix connection management details, and needs to be updated when SMTP connection caching is introduced.
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