Hello, We have discovered an issue in our postfix configuration that appears to limit the amount of recipients permitted in a single message to 100.
The issue exhibits itself in the form of our application receiving a timeout message after the 100th RCPT TO command and I have reproduced this using the Thunderbird mail client which also fails with a similar error [1]. I have read various documents and from what I can gather there is a process limit which defaults to 100 and also, according to the Tuning Guide the smtpd_recipient_limit option configures “The maximal number of recipients that the Postfix SMTP server accepts per message delivery request.” So I have a couple of questions; 1) Why is a message with multiple RCPT TO addresses apparently limited by the lower process limit value and not the smtpd_recipient_limit value? 2) Assuming that the OS [2] is configured correctly to allow a higher process limit and can cope with the load, are there any other negative implications of raising this limit to, for example, 1000, 5000 or 50,000? I.e. do I need to worry about overloading my clients mail servers? I see that delivery limits are configured elsewhere so I don’t think this will be an issue so I’m just checking. We do need to send bulk notifications to our clients so I’m looking for as high a value I can sensibly set which I can then pass on to our development team. Thanks in advance, Matt [1] Thunderbird error message. Sending of the message failed. The message could not be sent because the connection to Outgoing server (SMTP) my.email.server timed out. Try again. [2] OS & Postfix version. mail_version = 2.3.3 Linux my.email.server 2.6.18-400.1.1.el5 #1 SMP Thu Dec 18 00:58:32 EST 2014 i686 i686 i386 GNU/Linux
