Increase the max retry time (of soft bounces at least)
In case of soft bounce it can be expected that email should go through. The current maximum retry time of 8 hours is too short if there is lots of email sent. Retry time doesn't scale well in case if most email sending is done during the office hours. Morning emails might be dropped before the less trafic nightly hours. Below is an ESP throttling response from Hotmail
ESP throttling: X → Y 'Z' Server response: 421 421 RP-001 (BAY004-MC2F19) Unfortunately, some messages from IP weren't sent. Please try again. We have limits for how many messages can be sent per hour and per day. You can also refer to http://mail.live.com/mail/troubleshooting.aspx#errors.