External email appearance
When sending emails via JungleMail built-in mail server, even when using your own domain to do so, your Exchange Online Mail flow rules can modify your email subject or content and add External email warnings since emails are originating from outside your organization. To avoid this, you can edit your Mail flow rule and add an exception for emails delivered by JungleMail built-in mail server.
1. Navigate to your Exchange admin center and in the Mail flow section open Rules.
2. Open the rule that is managing your incoming emails from outside your organization.
3.Add an exception to the rule "The sender IP address is in any of these ranges or exactly matches" and add the JungleMail built-in mail server IP address to the exception.
IP for JungleMail for Office 365 (EU) app (service hosted in Europe):
IP for JungleMail for Office 365 (AU) app (service hosted in Australia):