Django and Mailgun : 552 sorry, your envelope sender domain must exist (#5.7.1)

Question

I'm trying to send mail using Django and Mailgun through the Anymail package and with an OVH server.

I'm currently receiving the 552 sorry, your envelope sender domain must exist (#5.7.1) error.

In this question/answer, it is suggested that I would need a "from" header, but the response I'm getting seems to show that the header is already included :

    "headers": {
      "to": "[email protected]",
      "message-id": "[email protected]",
      "from": "[email protected]",
      "subject": "Mail test !"
    },

Here is the full response, for reference :

{
  "severity": "permanent",
  "tags": [],
  "storage": {
    "url": "https://si.api.mailgun.net/v3/domains/mailgun.mydomain.fr/messages/eyJwIjpmYWxzZSwiayI6ImI5OGIyN2QzLTM2MmEtNGJjNi05ZWViLTRlMTA0NTVmYTIxMiIsInMiOiJlNmY5NzZhZTYwIiwiYyI6InNiaWFkIn0=",
    "key": "eyJwIjpmYWxzZSwiayI6ImI5OGIyN2QzLTM2MmEtNGJjNi05ZWViLTRlMTA0NTVmYTIxMiIsInMiOiJlNmY5NzZhZTYwIiwiYyI6InNiaWFkIn0="
  },
  "delivery-status": {
    "tls": false,
    "mx-host": "redirect.ovh.net",
    "attempt-no": 1,
    "description": null,
    "session-seconds": 0.9216420650482178,
    "code": 552,
    "message": "552 sorry, your envelope sender domain must exist (#5.7.1)",
    "certificate-verified": false
  },
  "recipient-domain": "mydomain-longversion.org",
  "event": "failed",
  "campaigns": [],
  "reason": "generic",
  "user-variables": {},
  "flags": {
    "is-routed": null,
    "is-authenticated": true,
    "is-system-test": false,
    "is-test-mode": false
  },
  "log-level": "error",
  "timestamp": 1473922798.282194,
  "envelope": {
    "transport": "smtp",
    "sender": "[email protected]",
    "sending-ip": "209.61.151.224",
    "targets": "[email protected]"
  },
  "message": {
    "headers": {
      "to": "[email protected]",
      "message-id": "[email protected]",
      "from": "[email protected]",
      "subject": "Mail test !"
    },
    "attachments": [],
    "recipients": [
      "[email protected]"
    ],
    "size": 643
  },
  "recipient": "[email protected]",
  "id": "TfJKwpoZQq6bM-MW5sm6nA"
}

And here is my Django code :

def SendTestEmail(request):
    if request.user.is_staff and settings.DEBUG == True :
        send_mail(
            subject='Mail test !',
            message='''Bonjour {}, votre email a bien été envoyé.'''.format(request.user.get_full_name()),
            recipient_list=['[email protected]',],
            from_email=settings.DEFAULT_FROM_EMAIL,
            fail_silently=False,
        )
        messages.success(request, 'Email correctement envoyé !')
    return redirect('rideshare_event_list')

Answer 1

Try using [email protected] as your from address instead of [email protected].

I'm afraid I'm not sure whether it's possible to use [email protected] as the from address.