Hi, I've been doing a bit of research into implementing quota based rejections for incoming messages with postfix. I want to do this before I hand it off to my LDA (which currently is handling the quota rejections) so that I can reject mail and stop sending backscatter when a recipient is over-quota.
I've not been able to find any mature, stable, and well maintained package available to do this with postfix, so I am looking into rolling my own solution. My environment uses quotas stored in mysql and manages quotas with dovecot. For my implantation, the following comes to mind so far: * Must be fast (to send a timely smtp response), for this reason, I'd likely use a daemon that caches quota limits from sql and reads stored quota sizes pre-calculated by dovecot whenever receiving a message. * Should be able to calculate the true message size, not simply trust any size headers sent. * Should handle multi-recipient messages somewhat gracefully. Optimally, I'd like to be able to deliver to everyone except for those over quota, and then reject with a "5.2.2 Mailbox full". My thought is, I'd still get the message to the intended recipients by re-injecting the message somehow, minus those recipients that are over quota. Also, I'd indicate in the rejection message that "only x, y, z.... users didn't receive the message" for the benefit of legitimate senders. >From what I've read, the three ways to implement such a system would be either as an smtp policy server, a before-queue milter, or a before-queue content filter. Finally, my questions are these: 1: Is there some package out there I may have missed that does this nicely? 2: Are these the only three candidate methods within postfix for implementing such a system? Have I missed anything? Does someone have a suggested alternative? 3: Of these candidate methods, which has the best potential performance, are there any with limitations that will preclude me from implementing the features I've mentioned? (I know I could read more on this one, but I'm looking for a small shortcut here please). 4: Are my ideas for multi-recipient handling too hacking or outlandish? Violate RFCs too egregiously? If I must, I could either patently reject the whole delivery, or silently discard the messages internally with some kind of notification message to the intended recipients instead. But, I don't want to stick with the current post-queue system that is filling my outbound queue with backscatter. Sorry for the length, just trying to be as comprehensive and concise as possible in my first posting. There is a lot in my mind right now on this project, so if I forgot to mention anything I'll elaborate further later. Please feel free to question my motives / assumptions / plans and suggest better alternatives. I want to do this right and not have some hack job. Thank you, Fred Kilbourn
