USER username@hostname proxyusername
    PASS password
    ACCT proxypassword

##</code><code>##

    1: USER user@remote.host

    2: USER fwuser
       ...
       USER user@remote.host

    3 and 4:
       USER fwuser
       ...
       USER user

    5: USER user@fwuser@remote.site

    6: USER fwuser@remote.site
       ...
       USER user

    7: USER user@remote.host
       ...
       AUTH fwuser