proc ::pop3::open {args} {
    variable state
    array set cstate {msex 0 retr_mode retr limit {} ssl 0}

    log::log debug "pop3::open | [join $args]"

    while {[set err [cmdline::getopt args {msex.arg retr-mode.arg ssl.arg} opt arg]]} {
if {$err < 0} {
    return -code error "::pop3::open : $arg"
}
switch -exact -- $opt {
    msex {
if {![string is boolean $arg]} {
    return -code error \
    ":pop3::open : Argument to -msex has to be boolean"
}
set cstate(msex) $arg
    }
    retr-mode {
switch -exact -- $arg {
    retr - list - slow {
set cstate(retr_mode) $arg
    }
    default {
return -code error \
":pop3::open : Argument to -retr-mode has to be one of retr, list or slow"
    }
}
}
ssl {
if {![string is boolean $arg]} {
return -code error \
":pop3::open : Argument to -ssl has to be boolean"
}
set cstate(ssl) $arg
}
    
default { ;# Can't happen 
        }
}
    }

    if {[llength $args] > 4} {
return -code error "To many arguments to ::pop3::open"
    }
    if {[llength $args] < 3} {
return -code error "Not enough arguments to ::pop3::open"
    }
    foreach {host user password port} $args break
    if {$port == {}} {
set port 110
    }

    log::log debug "pop3::open | protocol, connect to $host $port"

    # Argument processing is finally complete, now open the channel
if {$cstate(ssl)} {
package require tls
set chan [::tls::socket $host $port]
} else {
    set chan [socket $host $port]
}
    fconfigure $chan -buffering none

    log::log debug "pop3::open | connect on $chan"

    if {$cstate(msex)} {
# We are talking to MS Exchange. Work around its quirks.
fconfigure $chan -translation binary
    } else {
fconfigure $chan -translation {binary crlf}
    }

    log::log debug "pop3::open | wait for greeting"

    if {[catch {::pop3::send $chan {}} errorStr]} {
::close $chan
error "POP3 CONNECT ERROR: $errorStr"
    }

    if {0} {
# -FUTURE- Identify MS Exchange servers
set cstate(msex) 1

# We are talking to MS Exchange. Work around its quirks.
fconfigure $chan -translation binary
    }

    log::log debug "pop3::open | authenticate $user (*password not shown*)"

    if {[catch {
::pop3::send $chan "USER $user"
::pop3::send $chan "PASS $password"
    } errorStr]} {
::close $chan
error "POP3 LOGIN ERROR: $errorStr"
    }

    # [ 833486 ] Can't delete messages one at a time ...
    # Remember the number of messages in the maildrop at the beginning
    # of the session. This gives us the highest possible number for
    # message ids later. Note that this number must not be affected
    # when deleting mails later. While the number of messages drops
    # down the limit for the message id's stays the same. The messages
    # are not renumbered before the session actually closed.

    set cstate(limit) [lindex [::pop3::status $chan] 0]

    # Remember the state.

    set state($chan) [array get cstate]

    log::log debug "pop3::open | ok ($chan)"
    return $chan
}