After that, if you use your own server to send mail, it's up to you to configure your mail transfer agent (MTA) such as postfix or sendmail to queue and send out slowly to not get banned.
If you use SMTP like Amazon SES, you just have to get with your provider to increase or decrease your sending rate so that some aren't blocked from being sent if, let's say, XF throws out 1000 in a second and that'd exceed your per-second limit.