When you receive errors like < #5.1.1 smtp;550 5.1.1 RESOLVER.ADR.ExRecipNotFound; not found>, when you are sending emails and those email bounce back creating Non Delivery Recipients. You don’t know what to do and what is exactly going on with the error? I faced the same error for the first time.
Looking at the error codes given here (http://www.emailaddressmanager.com/tips/codes.html) it seemed “Bad Destination Mailbox”. But when I saw others were sending mails to that mailbox without any trouble. I searched for many forums but not succeeded. Finally, I got it resolved.
What causes this?
When you have shared your calendar to another contact, this usually creates issues and you may face similar kind of error messages.
Simply, unshare your calendar. And if you really want your invites to be shared with some other contacts? Make a rule that will forward your meeting requests to other contacts. This will resolve issues.