I have searched around for a good answer to my question but have yet to find one.
I deal with lots of Linux servers that send out newsletters. These servers are normally located at an office with a standard broadband connection. Sometimes a customer will send a newsletter with an attachment that may be a few MB in size. We do advise not to do this but they still so anyway.
What I am trying to achieve it a rate limit for postfix so it can only send out a small number of emails at any one time. By default postfix sends out loads in one go causing most to timeout half way though wasting loads of bandwidth. However sending just a few at a time will allow the emails to slowly flow out without saturating the connection and most emails failing to send. Most answers I have seen involve things like:
initial_destination_concurrency default_destination_concurrency_limit smtp_destination_concurrency_limit
However this applies to individual domains only and is not applied across the board.
I have however found this setting today
It looks like it does what I need by limiting the amount of smtpd daemons that can spawn allowing X amount of emails to leave. My question would be is this the best course of action and also does default_process_limit effect inbound connections as well? as I am worried changing this could stop servers receiving emails if all smtpd daemons are being used.
edit: all emails are submitted locally on the the server that are sending the emails.