Getting parameter validation error when sending emails through Mailgun API

Other Questions Mailgun
1

I’m trying to send an email using Mailgun’s PHP library but I keep running into issues. The error message says something about invalid parameters and sandbox domains. I’m not sure what I’m doing wrong here.

$emailService->dispatchMessage(EMAIL_DOMAIN, [
    'sender' => '[email protected]',
    'recipient' => EMAIL_LIST_ADDRESS,
    'title' => $messageTitle,
    'content' => $messageContent . '<br><br><a href="%unsubscribe_url%">Click to unsubscribe</a>'
]);

The exception I’m encountering mentions something about sandbox restrictions and authorized recipients. Has anyone faced this before? What could be causing this parameter validation to fail?

2

sounds like you hit the sandbox limit. you can only send to approved emails in that mode. make sure to add your recipients or upgrade for more flexibility. don’t forget to verify your sender domain too - placeholders won’t cut it.

3

Check your sender email format - it needs to match your verified domain exactly. That ‘[email protected]’ in your code looks like a placeholder you haven’t updated to your actual Mailgun domain. I hit the same parameter validation errors when my sender address didn’t match what I’d configured in Mailgun. Make sure your EMAIL_DOMAIN constant points to the correct domain you’ve set up, and verify the sender email uses that same domain. Also watch your recipient format - EMAIL_LIST_ADDRESS needs valid email addresses. The API’s pretty strict about parameter formatting and throws validation errors if anything’s off.

4

Mailgun’s API is a nightmare - all those validation rules and sandbox limits make it way harder than it needs to be.

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Saves me hours compared to manual API fixes.

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5

The sandbox domain is probably your problem. Mailgun’s sandbox only sends emails to recipients you’ve authorized in the dashboard. Go to your control panel, find the sandbox settings, and add the recipient email to the authorized list. If you’re ready for production, ditch the sandbox and set up your own domain instead. I had the exact same issue - spent hours debugging my code when it was just a config problem. Also double-check that your EMAIL_DOMAIN variable matches exactly what’s in Mailgun, including any subdomain stuff.

6

Parameter validation errors in Mailgun are usually authentication problems or wrong endpoint usage. I had the same issue - turns out I was mixing up my private and public API keys. Mailgun needs the private key for sending emails, so double-check you’re using the right one with proper permissions. Also verify your dispatchMessage method formats request headers and POST data correctly. Mailgun expects specific parameter names like ‘from’, ‘to’, ‘subject’, and ‘html’ - not custom ones like ‘sender’ or ‘title’. Your wrapper might handle the translation, but any mismatch will trigger validation errors before you even hit sandbox restrictions.