The following IP addresses are ones that Documo uses for various parts of the service. You may whitelist them as you see fit.
Webhooks
FTP/SFTP
Source/Cluster IP for Documo:
35.225.187.84
FaxBridge IP ranges:
vfb.faxATA.one
204.68.103.0/24
209.112.252.0/24
35.224.161.166
Mail provider sending IP:
23.253.182.165
Gateway IP (Fax Server IP):
4.30.4.189