We are getting the below error when sending to one of out customers. HAve done a search on it and can't find any info on it. Has anyone seen this? Please help shed som light with this issue.
There was a SMTP communication problem with the recipient's email server. Please contact your system administrator.
<phoradbefp1.us.ecc.ads #5.5.0 smtp;553 sorry, your envelope sender is invalid (#5.1.8)>