Every mail failed to send with error message: Validation failed for ...

I you get error message like this in your outbox:

Validation failed for: Affiliate program superAff.com <some@email.com>

Look closely to this line to word superAff.com. You see that little red dot there? Yes, and that is the main problem. Because some SMTP servers are configured that way, thay can't recognize address enclosed in < > brackets in from field, if it contians string with dot before email address enclosed in < >.

To resolve this problem you could rename your affiliate program, so it won't contains dot character. Or you can write to your SMTP server, if they can recofigure server it can handle string like "Affiliate program superAff.com <some@email.com>" fin field from address, and parse right email from there.