When sending mail from MailGun, I get "Sender address rejected: Domain not found"

I have 2 domains setup in Mail In A Box, but I am unable to send mail to them using MailGun. any other provider seems fine .e hotmail.com

Error: “Sender address rejected: Domain not found”

Any ideas?

Cheers
Murray

perhaps you forgot to add their custom DNS?

  1. to merge its SPF with the default one into your ‘custom DNS’ panel for your domain:

yourdomain.com TXT v=spf1 include:mailgun.org ~all

  1. to add their TXT DKIM record to your ‘custom DNS’ panel for your domain