• If you manage your own SMTP servers, you will need to get a certificate signed by a recognised CA, and identify it with the domain name you use in your SMTP configuration.
• If you get your service from a major email provider, they will not be using self-signed certificates, but they may be sharing the server between many customers, allowing each customer to use a custom domain name pointing to the same machine.  The solution for that is to get the canonical name from the provider to use in your SMTP settings.  
  • It is rare, but it is possible that the server will use a different certificate on different ports, so switching between 465, 587 and 25 might yield better results.  Again, the best source for the settings is your email provider.

If you see one of these error messages, you might need to select a different port number and authentication type. Make sure you have used the correct outgoing mail server for your provider. You might need to contact your third party email provider for the correct settings.

Select a secured connection

Check with your other mail service for their recommended port number, authentication type, or outgoing mail server. Make sure your third party provider supports SSL or TLS with a valid certificate. Here are some common combinations:

• SSL with port 465
• TLS with port 25 or 587