Hello@Glen_R ,

Thanks for contacting our community.

Here are some suggestions for your case:
1. Double-check the format of the whitelist entries: Ensure you are entering the correct domain names (e.g., smtp.example.com) and not just the base domain. Try adding both the whole SMTP server domain and any related subdomains.
2. Test with Parental Controls disabled: As you mentioned, the email sends successfully when Parental Controls are off, which confirms the router is blocking the SMTP traffic.
3. Consider using Access Control instead: If your goal is to restrict general internet access but allow specific applications, you might find Access Control (found under Advanced > Security > Access Control) more flexible. You can use Blacklist mode to block internet access for certain devices, or Whitelist mode to only allow specific devices.