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Postfix: The Definitive Guide by Kyle D. Dent

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Testing Your Authentication Configuration

It's probably best to try authenticating to your SMTP server manually before having your users attempt it with their email clients. By connecting to your SMTP server and manually authenticating, you can see exactly what response you get, and you can immediately check your log file for any other important information.

The easiest way to connect to your SMTP server is to use a Telnet client and then start speaking SMTP to your server. (Chapter 2 shows a sample SMTP session.) The PLAIN mechanism is the easiest to test, so if you have disabled it, you may want to enable it just to confirm that authentication works. You can disable it after you are finished testing.

To authenticate using the PLAIN mechanism, you must send the command AUTH followed by your credentials encoded using base64. Your credentials are a combination of the authorization identity (identity to login as), followed by a null character, followed by the authentication identity (identity whose password will be used), followed by a null character, followed by the password. Usually, the authorization identity is the same as the authentication identity, and we'll assume as much here. Using the credentials for the user kdent, you need to encode the string 'kdent\0kdent\0Rumpelstiltskin'.

The tricky part is to encode your credentials in base64 without including a carriage return character. If your system has the mmencode and printf commands, it should be simple. The printf command ...

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