Mailgun keep using sandbox domain instead my custom domain

Here is my production configs:

 "mail": {
    "from": "nomad <noreply@mydomain>",
    "transport": "SMTP",
    "options": {
      "service": "Mailgun",
      "host": "",
      "secureConnection": false,
      "port": 587,
      "auth": {
        "user": "postmaster@mydomain,
        "pass": "***password***"

But when I try to publish a post, I received this error:

NAME: EmailError
MESSAGE: The server has encountered an error.

level: normal

"The email service was unable to send an email batch."
Error: Domain sandboxf9cbaee596aa43579df6c4*** is not allowed to send: Sandbox subdomains are for test purposes only. Please add your own domain or add the address to authorized recipients in Account Settings.
    at /var/www/netwalker/versions/4.36.0/core/server/services/bulk-email/bulk-email-processor.js:245:30
    at IncomingMessage.<anonymous> (/var/www/netwalker/versions/4.36.0/node_modules/mailgun-js/lib/request.js:327:17)
    at IncomingMessage.emit (events.js:412:35)
    at endReadableNT (internal/streams/readable.js:1334:12)
    at processTicksAndRejections (internal/process/task_queues.js:82:21)

and when I try to send a test mail for myself, it’s succesfully but the email was sent from this address : so I think Mailgun is using the sandbox domain instead my custom domain.
Anyone have an idea to fix this problem ?