The recommended way of doing this is to white list the whole doodle.com domain, and configure your email solution to check the SPF records to determine if a host is a valid sender. This way you don't have to modify your configuration whenever we change our email delivery setup.
If your email solution does not allow this, you can still white-list our IP address ranges:
- 149.72.180.54
- 168.245.95.11
- 168.245.78.192
- 168.245.10.81
- 168.245.120.5
- 168.245.114.108