My organization sends membership renewal emails using NetMail and e-newsletters through another service.  While comparing the click-through rates between the two services recently, I noticed that some member email addresses which are returning opens, click-throughs, and donations from the other service's emails are simultaneously hard-bouncing emails from NetMail with the message "Invalid Email Recipient - email@domain.com".

Has anyone else experienced this?  I appreciate the convenience of downloading renewals directly to Raiser's, but it isn't worth it if the renewal notices aren't even reaching our members and their good email addresses are being incorrectly marked as bad in our system.