Having a new error message at a site running OE (200521) when trying to email out invoices. Starting today they are receiving the error message:
"There was an error attempting to send the email: <emailaddress>... Relaying denied: You must check for new mail before sending mail".

We've checked for mail, and have tested by sending emails from the client's mail client without issue. We've also performed the email test from within OE and Sales CQ without issue and they do appear in the inbox as expected.

Any thoughts?