The ‘403 forbidden’ error indicates that the account you’re trying to authenticate in your SMTP plugin doesn’t have the correct permission to send emails.
It often occurs when sending emails using SendGrid SMTP services. If the API key on your SMTP plugin doesn’t have mail sending capabilities, you’ll likely encounter this error.
Resolving the Error – Solution
To fix the ‘403 forbidden’ error, you’ll need to check and update your API key permission settings.
To check that your API key has the correct access level, log in to your SendGrid account and navigate to Settings » API Keys.
This will bring you to a page with all your available API keys. Click the Settings gear icon and select Edit API Key for your SMTP plugin’s API key.
After that, additional permissions will appear for you to configure. Scroll down to the Mail Send setting and be sure the permission level is set to Full Access.