I have a Mailman 3 server up and running but I'm terrified to migrate to it from my existing Mailman 2 provider for fear that services like Gmail will randomly start blacklisting my IP with little I can do about it. I have SPF records set up so I'm hoping I'll be Ok but I'd like to have a backup plan.
Has anyone ever tried using an external service like Mailgun or Sendgrid as a relay? I tried both but couldn't get either to work due to their sender authentication mechanism. They want all 'From:' headers to be from domains that are pre-authenticated as senders. But Mailman keeps the 'From' header from the original sender so it won't match any authenticated domains. Right?
Is there anything to be done here or do I just have to migrate and pray?