I'm using dovecot & postfix to bring smtp auth to our customers. Normal mail clients have no problem at all and I'm so satisfied.

However, we're having problems with Microsoft Exchange server clients. We're using our postfix-dovecot server as smarhost for several Exchange Servers, and we wish to use TLS + basic authentication for these outgoing mails.

But it seems that the way Exchange talks to our server, dovecot gets confused, and password is used instead username for user lookups, so authentication fails.

Info: auth(default_with_listener): client in: AUTH 5       login   service=smtp    resp=bXlfdXNlcm5hbWU=           //(resp=my_username)
Info: auth(default_with_listener): client out: CONT        5       VXNlcm5hbWU6     //(Username:)
Info: auth(default_with_listener): client in: CONT 5       bXlfcGFzc3dvcmQ=         //(my_password)
Info: auth(default_with_listener): client out: CONT        5       UGFzc3dvcmQ6               //(Password:)
Info: auth(default_with_listener): client in: CONT 5       bXlfcGFzc3dvcmQ=              //(my_password)
Info: auth(default_with_listener): sql(my_user): query: SELECT user, password FROM users WHERE user = 'my_password'
Info: auth(default_with_listener): sql(my_user): unknown user
Info: auth(default_with_listener): client out: FAIL        5       user=my_password

Any clue if there is a way to make it work, either modifiying Exchange or dovecot settings?

Thank you very much!