When you send an email to a contact you receive a non-delivery report (NDR) with the following error:
Remote SMTP Server Returned: 553 mailbox firstname.lastname@example.org is restricted
Read more [[You receive non-delivery reports (NDR) when you send an email]].
There is a problem with your contact’s mail server.
We are unable to resolve this issue as it is not part of the DomainsFoundry network.