If you receive the following error message when attempting to send emails:
Validation failed for: Affiliate program superAff.com <some@email.com>
Pay close attention to the part that reads superAff.com. Notice the full stop (period)? This is likely the source of the problem. Certain SMTP servers cannot process an address enclosed in < > brackets in the From field if there is a full stop immediately before the email address. This can cause your emails to fail validation and not be sent.
To resolve this issue, you can either rename your affiliate program to ensure it does not contain the full stop, or you can contact your SMTP provider to request a configuration change. The server should be able to handle strings like "Affiliate program superAff.com <some@email.com>" in the From field and correctly parse the email address.