#!/bin/sh

# checkmail 1.0.12 (1999-May-16-Sun)
# Adam M. Costello <amc@cs.berkeley.edu>
#
# Given a list of email addresses on stdin, one per line, checkmail
# checks the mail status for each one (following forwarding chains, but
# not trees), and prints the results to stdout in the format
#
# + OriginalEmailAddress <FinalEmailAddress>
#   MailStatus
#
# MailStatus may be more than one line, but each will begin with two
# spaces.
#
# There may also be various warning messages sent to stderr, composed of
# lines beginning with "! ".
#
# checkmail depends on awk, egrep, finger, grep, hostname, nslookup,
# ping (or fping, see below), sed, sort, telnet, and tr being in PATH.
#
# With the -q option, the MailStatus is not collected, saving time.


# Time limits (in seconds):
fingerlimit=20
telnetlimit=20

# Ping method:
#ping=ping           # Use this if "ping <hostname> <timeout>" works.
ping=ping_via_fping  # Otherwise use this (requires fping).

# My hostname:
myhostname=`hostname`
myhostname=`
  echo "$myhostname" |
  nslookup 2>&- |
  awk '/^Name:/ {print $2}'
`

if [ "$1" = -q ]; then
  quick=yes
  shift
fi

[ $# -eq 0 ] || {
  echo "usage:" >&2
  echo "$0 [ -q ]" >&2
  exit 1
}

debug() {
  echo "# $1" >&2 # Comment this out to turn off debugging.
  :
}

ping_via_fping() {
  fping -r${2-20} -t1000 $1
}


# timelimit <limit> <cmd> [ <arg> ... ]
#
# Runs the command in the background, killing it after <limit> seconds.

timelimit() {
  limit=$1
  shift
  "$@" &
  pid=$!
  { sleep $limit; kill $pid 2>&-; } >&- &
}


# followaddr <user> <host> [ <addr> ... ]
#
# Checks whether mail to <user>@<host> gets forwarded.  If so, follows
# the forward chain to the final address, which is printed to stdout.
# Additional arguments containing all addresses that have been followed
# (including the one being passed this time) are used to detect loops.
#
# If there is a problem, it will print a short error message to stdout
# and return unsuccessfully.

followaddr() {
  user=$1
  host=$2
  address=$user@$host
  debug "following address $address"

  [ $# -le 50 ] || {
    echo "! Forward chain too long: $*" >&2
    return 1
  }

  exchangers=`
    { echo "set qt=mx"; echo $host; } |
    nslookup 2>&- |
    grep 'mail exchanger' |
    sort +3 -4n |
    awk '/mail exchanger/ { printf "%s ", $NF }'
  `

  [ -n "$exchangers" ] || {
    echo "! No mail exchanger for $host, will use $host" >&2
    exchangers=$host
  }

  debug "exchangers are $exchangers"

  for exchanger in $exchangers; do
    if $ping $exchanger 5 >&- 2>&-; then
      response=`
        { echo "HELO $myhostname"
          echo "EXPN $user@$exchanger"
          echo "EXPN $user"
          echo "VRFY $user@$exchanger"
          echo "VRFY $user"
          echo quit
        } | timelimit $telnetlimit telnet $exchanger 25 2>&-
      `
      forwards=`sed -e '1,/^.[05]. / d' -e '/^25[01]/ !d' \
                -e 's/.*<\([^>]*\)>.*/\1/' -e 's/^[ 	]*//' \
                -e 's/[ 	].*//' -e 's/^\\\\//' << EOF
$response
EOF
      `

      if [ -z "$forwards" ]; then
        echo "! Cannot expand $user at $exchanger" >&2
        [ -z "$response" ] || sed -e 's/^/! > /' >&2 << EOF
$response
EOF
        nexthop=
      else
        nexthop=`sed -e '/|/ d' -e q << EOF
$forwards
EOF
        `
        break
      fi
    else
      echo "! Cannot reach $exchanger" >&2
      nexthop=
    fi
  done

  debug "nexthop is <$nexthop>"

  if [ "$nexthop" = "$user" -o "$nexthop" = "" ]; then
    echo $user@$exchanger
    return 0
  fi

  shift 2
  history=$*

  oldIFS=$IFS
  IFS=@$oldIFS
  set -- $nexthop
  IFS=$oldIFS
  nextuser=$1
  nexthost=$2

  case $nexthost in
     "") nexthost=$exchanger
         debug "expanded $nexthop to $nextuser@$nexthost"
         ;;
    *.*) ;;
      *) rawnexthost=$nexthost
         nexthost=`
           { echo "set domain=$host"; echo "$nexthost"; } |
           nslookup 2>&- |
           awk '/^Name:/ {print $2}'
         `
         [ -n "$nexthost" ] || {
           echo "! Unable to resolve host $rawnexthost" >&2
           return 1
         }
         debug "resolved $rawnexthost to $nexthost"
         ;;
  esac

  nexthop=$nextuser@$nexthost

  if [ "$nexthop" = "$user@$exchanger" -o "$nexthop" = "$address" ]; then
    echo $user@$exchanger
    return 0
  fi

  for addr in $history; do
    [ "$nexthop" != "$addr" ] || {
      echo "! Mail loop detected: $history $nexthop" >&2
      return 1
    }
  done

  followaddr $nextuser $nexthost $history $nexthop
}


# fetchmailstatus <address>
#
# Returns lines, each beginning with two spaces, containing mail status
# information about <address>, which must have the form user@host, and
# should be a final address (as returned by followaddr).

fetchmailstatus() {
  address=$1
  oldIFS=$IFS
  IFS=@$oldIFS
  set -- $address
  IFS=$oldIFS
  user=$1

  timelimit $fingerlimit finger -l $address 2>&- |
  tr -d '\015' |
  awk '
    /[^a-zA-Z]'$user'[^a-zA-Z]/ { count = 1; }
    count > 10 { exit; }
    count >= 1 { if (match($0, /[Mm]ail|[Uu]nread/)) print "  " $0;  ++count; }
  '
}


# Main loop.

while read address; do
  oldIFS=$IFS
  IFS=@$oldIFS
  set -- $address
  IFS=$oldIFS
  [ $# -eq 2 ] || {
    echo "! Bad address (wrong number of @ signs): $address" >&2
    continue
  }

  if finaladdr=`followaddr $1 $2 $1@$2`; then
    debug "address is $address"
    debug "finaladdr is $finaladdr"
    echo "+ $address <$finaladdr>"
    [ $quick ] || {
      mailstatus=`fetchmailstatus $finaladdr`
      [ -z "$mailstatus" ] || echo "$mailstatus"
    }
  else
    echo "+ $address ERROR"
  fi

  echo ""
done