Linux Email Postfix – How to Rate Limit Outgoing Concurrent Connections

concurrencyemaillinuxpostfixrate-limiting

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 1.2.3.4. 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 user@company1.com and user@company2.com, 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?

Best Answer

Yes postfix is clever enough to deliver the messages to the two domains user@domain1.com and user@domain2.com. 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.

Related Solutions

Linux – How to rate-limit outgoing email on Linux/Postfix host

I gave up on using postfix to solve this problem. Instead, I found a relatively clean way to solve the problem using MH, which is the mailer I have been using for over 15 years:

An outgoing mail that should be delayed by N hours is composed in the MH "draft folder" +delayN.
When I have finished composing the mail, to ensure that I leave the mail in the folder instead of sending it, I have a modified whatnow program that treats send as a synonym for quit if the message is stored in a folder whose name has the form delayNNN, where NNN is a nonempty sequence of digits.

My hourly cron job checks all relevant folders and ships files that are old enough (details elided):

for path in $MAIL/delay*[0-9]
do
  minutes=...
  for outgoing in $(find $path -mmin +$minutes -name '[0-9]*')
  do
    folder=... 
    msg=...
    send -draftfolder +$folder -draftmessage $msg
  done
done

How to rate limit outgoing SMTP connections for Postfix

Look at "policyd" for Postfix. That should be able to fix your ratelimiting. That said, 10 SMTP connections per minute seems stupidly low, and I'd challenge the provider on that (600 per hour may be reasonable)

Best Answer

Related Solutions

Linux – How to rate-limit outgoing email on Linux/Postfix host

How to rate limit outgoing SMTP connections for Postfix

Related Topic