If you're sending through Mandrill's SMTP integration, you may see "Relay Access Denied" or "Unable to Connect to Host" errors when you're just getting started. These errors can have various causes, so we'll cover some of the most common causes and suggest troubleshooting tips in this article.
- Make sure your hosting provider or internet provider (ISP) allows outbound SMTP connections. Some shared hosting providers only allow outbound SMTP connections on dedicated servers, while others block them completely. In some cases, hosting providers might redirect the connection, so instead of connecting to smtp.mandrillapp.com, you connect to their local server instead.
- Make sure the port you've selected is one that your hosting provider or ISP has available for outbound SMTP connections. Some hosts block all connections on port 25, for example, so you can try using a different supported port.
- Double check that you're using a valid API key to connect via SMTP, and not the password that's used to log in to Mandrill's web application.
- If you're using Postfix, make sure that you have an SASL library (like libsasl2 or cyrus) installed and that it's up to date. Otherwise, you may be connecting but not passing authentication credentials.
- For other SMTP libraries, make sure you're using LOGIN or PLAIN authentication methods.
Once you've confirmed all of the above, if you're still seeing issues, please enable additional logging in your SMTP program or library. If you're using an integration, contact the integration developer for information on configuring logging of the SMTP conversation.