There is already the BULK_MAILS_PER_CYCLE constant to solve issues with hosts that have trouble with many emails at once.
Equally, if not more important, is how many emails are sent in a given timeframe. It’s normal for hosts and email services to have some kind of limit in that regard, but with the way IPS sends out bulk mail, it unpredictable when these limits are being hit and there is no way around this problem when the limits are hit.
I suggest a solution like a MAX_MAIL_CYCLES_PER_TASK constant or setting to limit the amount of cycles run each time a cron is being fired. So, for example, I could set 1 run of 100 emails with the cron running every minute resulting in 1000 mails in 10 minutes.
I understand that IPS isn’t all that focussed on features that would only help self-hosted customers, but it seems like an easy implementation which could help a lot of users. It’s actually the behaviour that people are already expecting.