: start( helo_domain = <local host name>, account = nil, password = nil, authtype = nil )
: start( helo_domain = <local host name>, account = nil, password = nil, authtype = nil ) {|smtp| .... }
    TCP ͥĥꡢƱ SMTP å򳫻ϤޤΤȤ
    ΥۥȤ FQDN  helo_domain ˻ꤷޤ
    ⤷Ǥ˥å󤬳ϤƤ IOError ȯޤ

    account  password ξͿ줿硢AUTH ޥɤˤä
    ǧڤԤޤauthtype ϻѤǧڤΥפǡܥ
     :plain  :cram_md5 ꤷޤ

