SMTP send problem

[Exploding5heep]

I've installed the 0.5.3 release of roundcube and can't get smtp to work correctly. The imap login is fine, and smtp works fine from clients like Thunderbird.

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SMTP send:  NOT OK(Authentication failure: Invalid response code received from server (Code: 535))

is the exact error message the web installer gives.

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Jun  6 17:52:08 XXX postfix/smtpd[22787]: connect from localhost.localdomain[127.0.0.1]
Jun  6 17:52:08 XXX postfix/smtpd[22787]: setting up TLS connection from localhost.localdomain[127.0.0.1]
Jun  6 17:52:08 XXX postfix/smtpd[22787]: Anonymous TLS connection established from localhost.localdomain[127.0.0.1]: TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)
Jun  6 17:52:08 XXX postfix/smtpd[22787]: warning: SASL authentication failure: no secret in database
Jun  6 17:52:08 XXX postfix/smtpd[22787]: warning: localhost.localdomain[127.0.0.1]: SASL DIGEST-MD5 authentication failed: authentication failure
Jun  6 17:52:08 XXX postfix/smtpd[22787]: disconnect from localhost.localdomain[127.0.0.1]

This is from the mail log. XXX was the hostname.

Any ideas as to what might cause this?