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

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": "evenements#mydomain-longversion.org",
"message-id": "20160915065953.15168.46300.4ABD80EB#mailgun.mydomain.fr",
"from": "covoiturage#mydomain.fr",
"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": "postmaster#mailgun.mydomain.fr",
"sending-ip": "209.61.151.224",
"targets": "evenements#mydomain-longversion.org"
},
"message": {
"headers": {
"to": "evenements#mydomain-longversion.org",
"message-id": "20160915065953.15168.46300.4ABD80EB#mailgun.mydomain.fr",
"from": "covoiturage#mydomain.fr",
"subject": "Mail test !"
},
"attachments": [],
"recipients": [
"evenements#mydomain-longversion.org"
],
"size": 643
},
"recipient": "evenements#mydomain-longversion.org",
"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=['evenements#mydomain-longversion.org',],
from_email=settings.DEFAULT_FROM_EMAIL,
fail_silently=False,
)
messages.success(request, 'Email correctement envoyé !')
return redirect('rideshare_event_list')

Answer 1

Try using covoiturage#mailgun.mydomain.fr as your from address instead of covoiturage#mydomain.fr.
I'm afraid I'm not sure whether it's possible to use covoiturage#mydomain.fr as the from address.