550 validating sender outlook
For steps to create, copy, and manage mail flow rules, see Manage mail flow rules.
For each rule, you have the option of enforcing it, testing it, or testing it and notifying the sender.
Does this happen to the same (limited number) of receiving domains or to all domains? how to find our domain or ips are black listed or gray listed and if i found tht they are..
You can use mail flow rules (also known as transport rules) to identify and take action on messages that flow through your Exchange Online organization.
You can choose to do nothing about DKIM for your custom domain too.
However that e-mail address doesn’t exist on the Remote mail server, so it’s always going to fail and cause a bounce-back error.
Typically these types of bounceback errors are hard bounces, meaning that trying to send the message again won’t be successful.
For example, the below bounce specifies: Envelope-to: [email protected]: Thu, -0400Received: from mailnull by ecbiz103.with local (Exim 4.77)id 1TRUGT-0005Qd-RTfor [email protected]; Thu, -0400X-Failed-Recipients: [email protected] Auto-Submitted: auto-replied From: Mail Delivery System This message was created automatically by mail delivery software.
A message that you sent could not be delivered to one or more of itsrecipients. The following address(es) failed: [email protected] No Such User Here —— This is a copy of the message, including all the headers.