How I should configure SMTP?

[iskycc]

Hello, may I ask how I should configure SMTP? I follow the general configuration method, and the following error will be displayed when I send an email with forgotten password:

Postmark::ApiInputError: No Account or Server API tokens were supplied in the HTTP headers. Please add a header for either X-Postmark-Server-Token or X-Postmark-Account-Token.

Can you give me an example, such as SMTP whether to add a port.Or tell me what is the cause of the above error and how to solve it.

And...Can I send a password reset email with mailgun, and if so can you give a sample configuration file?