If you use an internally-hosted mail server, you must grant access to OnceHub by allowing the following server IP addresses:
- 52.184.200.53
- 52.177.197.227
- 13.77.100.95
- 52.177.198.87
- 52.225.219.177
- 52.225.218.66
- 52.177.199.129
- 13.68.89.72
- 40.84.2.28
- 104.209.238.147
- 40.123.38.105
