In a prior forum discussion on May 14, 2018, an entity had problems with email throttling resulting in mail flow issues. In August, 2019, we have also seen this problem and need assistance in validating the throttling of services provided through MessageLabs. The Tier 2 Senior Product Support Engineer that resolved the prior forum issue is Ian Tiller.
The external IPs in question are:
199.16.160.4
199.16.160.6
199.16.164.8
199.16.164.9
Thanks for the assistance