I need to limit postfix outgoing connections for specific mailservers, but it seems to me that posfix's limiting is based on domains? What if there is one mailserver for more domains? I tried to find out what "destination" means in postfix's tuning manual, but it seems that it is the recipient's domain instead of the mailserver (I may be wrong though)

Current situation: I have a mailserver mail.example.com with IP This mailserver is hosting emails for company1.com and company2.com.

When I set:

smtp_destination_concurrency_limit = 1
default_destination_concurrency_limit = 1

Now, if I send two emails at once - to [email protected] and [email protected], is postfix clever enough to get MX servers for both emails, see that the mail server is identical and limit the connections, or does postfix see 2 different domains and let it go together in two concurrent connections?

2 Answers 2


Yes postfix is clever enough to deliver the messages to the two domains [email protected] and [email protected]. Before postfix starts querying DNS entries to get MX records. Postfix first attempts to deliver the message internally. Seeing the current server holds for two domains emails will successfully be delivered to the account respectively.


Same problem here with Orange. Two domains but one MX with bad temper (dont like to work too hard...).

The answer to your question seems to be : NO. Postfix isn't clever and concurrency limit is just based on destination domain not on MX...

So, in my case, postfix isn't able to slow down and many emails are rejected because it dont know that orange.fr and wanadoo.fr are relayed by the same dumb MX.

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