I run a GNU Mailman list for an organization. The list is hosted on an Amazon EC2 instance and for years, I had no trouble sending email to list members directly from the EC2 instance. Then one day, list members who were using @shaw.ca email addresses were no longer receiving emails from the list. Shaw started blocking email from the instance. So then I started running the email through Amazon SES which seemed to work – except that Mailman exceeded Amazon SES’ sending limits. The account was limited to 14 emails per second which is not hard to exceed.
Despite all the configuation settings, there is no way to throttle email sending in Mailman. Google searches did not turn up anythig useful. In the end, I just went into /usr/lib/mailman/Mailman/Handlers/SMTPDirect.py and used a call to time.sleep( 0.10 ) just before sending an email to limit it to a maximum of 10 emails per second.