MX needs 12 seconds per 1000 different remote destinations.
smtp process limit = 100, bundle_recipients = 0.
/usr/bin/time ./smtp-source -r 1000 fist
1.13 real 0.07 user 0.27 sys
Jun 8 13:32:18 fist mx:smtpd[18174]: connect from spike.porcupine.org(168.100.1
Jun 8 13:32:31 fist mx:smtp[18209]: 085688: to=<544foo@spike.porcupine.org>, re
Total time: 13 seconds
/usr/bin/time ./smtp-source -r 2000 fist
2.55 real 0.21 user 0.48 sys
Jun 8 13:33:23 fist mx:smtpd[18174]: connect from spike.porcupine.org(168.100.1
Jun 8 13:33:48 fist mx:smtp[18184]: 085693: to=<1041foo@spike.porcupine.org>, r
Total time: 25 seconds
/usr/bin/time ./smtp-source -r 5000 fist
[test generating machine ran out of resources while receiving mail]
/usr/bin/time ./smtp-source -r 1000 fist
1.38 real 0.17 user 0.16 sys
Jun 8 15:20:33 fist mx:smtpd[27695]: connect from spike.porcupine.org(168.100.1
Jun 8 15:20:46 fist mx:smtp[27724]: 085687: to=<493foo@spike.porcupine.org>, re
Total time: 13 seconds
/usr/bin/time ./smtp-source -r 2000 fist
2.64 real 0.23 user 0.46 sys
Jun 8 15:20:52 fist mx:smtpd[27695]: connect from spike.porcupine.org(168.100.1
Jun 8 15:21:16 fist mx:smtp[27743]: 085687: to=<1086foo@spike.porcupine.org>, r
Total time: 24 seconds
/usr/bin/time ./smtp-source -r 5000 fist
[test generating machine ran out of resources while receiving mail]