A "frequent basis" is whatever LP decides it is, at the moment! They do advise you to stay under 300 per hour for regular email from your site. What I can't determine from the mailman description is whether this thing is running on your account, and is subject to the 300 per hour advice (400 absolute limit), or it's running "centrally" and you're just buying the right to use it a certain amount (first share free, additional ones $$). LP bars "background processes" on shared server accounts, so I would suspect that you're not actually running mailman on your own account. Anyone know for sure?

Anyway, averaging one overage a month is probably skating on thin ice. Sooner or later you'll have another hot topic and this time you'll be suspended. If mailman can't be throttled, you'll have to look at other options. It seems rather odd that LP would offer a mailing service, and then restrict it so much. If it were running on your account, and you had full access to the source (Python and C), you might be able to add a "sleep" call after each email send (12 seconds * number of recipients, to stay under 300 per hour). Failing that, I doubt that there are any mailman-like products out there that could run on a shared server, because of the ban on background processes. Perhaps something on a cron job that wakes up every few minutes to read the mail queue and send out the post? Maybe a filter on the mailbox to kick off the process every time a mail comes in? There might be something that works one of those ways (unless LP objects to it).

You also might consider whether a mailing list is the most efficient way to run a discussion group. Pre-World Wide Web, they were the only game in town, but now there are many nice web-based forums such as SMF and phpBB.

Am I correct in assuming that mailman is not installed into your account itself, but is a shared central resource? You'd think that someone would get around to patching it to throttle the number of emails per hour per account, rather than lying in wait for you to exceed some cap and then jumping up and yelling, "gotcha!" It appears to be currently supported -- I wonder if anyone has bothered to ask for such a feature?

A little more flexibility in allowing brief load spikes once in a while would be nice, but I get the impression that if such a feature isn't already in the canned server management software that LP uses, they don't dare to mess with the code to add it.

Since PHPlist is one-way (outbound only), I'm surprised that LP would recommend it for a mailing list. If your mailing list always sends to the same addresses, perhaps something could be done to have the mailing list just mail to one address (at your site) and have something there remail it via PHPlist? Clumsy (especially when you have to manually maintain the address list on the PHPlist side), but at least you'd get the ability to throttle the rate. The other alternatives would be to keep looking for some mailing list software (with email send rate throttling, or output to PHPlist) that either runs on cron or as a mailbox filter. I'd be surprised if one or the other doesn't exist somewhere.