What are the SMTP details / API Tokens I should be using?

If you're using API: 

• Use the Server Token which is found in your Postmark account by going to Server > API Tokens. The Server Token is unique for each server you create in Postmark.
• In order to send through a specific message stream, you need to add a “MessageStream” parameter that references a stream ID. If no Stream ID is provided when sending, Postmark will send through the default Transactional Stream.

Find out why it's important to make sure you're separating transactional from broadcast messages.

If you're using SMTP:

• Server — smtp.postmarkapp.com (for transactional messages) and smtp-broadcasts.postmarkapp.com (for broadcast messages)
• Ports — 25, 2525, or 587
• TLS — TLS is available via the STARTTLS SMTP extension. This establishes an encrypted connection to our SMTP server, and all Tokens and content are encrypted while they are transmitted to us. We recommend you use TLS if possible.

From here, there are two authentication options to choose from, depending on what your SMTP client offers. The only difference between them is the configuration.

• API Token + Header — Use the Server API Token and Header which can be found by clicking on a server, then a message stream and then Settings. The Server API Token acts as the Username and Password. The Header allows you to specify the message stream through which email should be sent. If a Header is not specified, Postmark will use the default transactional stream.

OR

• Use an SMTP Token. An SMTP Token consists of an Access Key (which acts as a username) and a Secret Key (which acts as a password). The Secret Key should be stored in a safe place since after it has been generated, it's no longer visible. If you need access to this again, you'll need to generate a new SMTP Token for authentication. SMTP Tokens are unique for each message stream.
  

For more information on using SMTP, please review our developer docs.

If you are using Postfix to send through Postmark you can follow our Instructions for getting set up in our guide Can I configure Postfix to send through Postmark?