email_test.sh

#!/bin/sh
############################################################ IDENT(1)
#
# $Title: Script to test if an e-mail address is valid $
#
############################################################ GLOBALS

pgm="${0##*/}" # Program basename

#
# Global exit status
#
SUCCESS=0
FAILURE=1

#
# Command-line options
#
TELNET=     # -t
VERBOSE=    # -v

############################################################ FUNCTIONS

usage()
{
    echo "Usage: $pgm [-tv] username@server.com" >&2
    exit $FAILURE
}

############################################################ MAIN

#
# Process command-line options
#
while getopts tv flag; do
    case "$flag" in
    t) TELNET=1 ;;
    v) VERBOSE=1 ;;
    *) usage # NOTREACHED
    esac
done
shift $(( $OPTIND - 1 ))

[ "$1" != "${1#*@}" ] || usage # NOTREACHED

#
# Expect code to talk to the mail server (MX)
#
export TELNET
exec 9<<'EOF_EXPECT'

    ################################################## PARENT GLOBALS

    set email   $env(email)
    set domain  $env(domain)
    set mx      $env(mx)
    set port    $env(port)
    set telnet  [expr {$env(TELNET) != ""}]

    ################################################## GLOBALS

    set timeout 300

    if {$telnet} {
        set spawn_cmd   "telnet"
    } else {
        set spawn_cmd   "nc"
    }

    ################################################## MAIN

    fconfigure stdout -buffering none
    spawn {*}$spawn_cmd $mx $port

    expect -re {220} { send "helo hi\n" }
    expect -re {250} { send "MAIL FROM: <root@localhost>\n" }
    expect -re {250} { send "rcpt to: <$email>\n" }
    expect -re {(250|550)} { send "quit\n" }
    expect -re {221 .* closing connection}

EOF_EXPECT
EXPECT_CMD=$( cat <&9 )
export EXPECT_CMD

#
# Get the mail server (MX) for the email domain
#
export email="$1"
export domain="${email#*@}"
mx=
for m in $( host -t MX "$domain" |
    awk '/mail is handled by/{sub(/\.$/, "", $NF); print $NF}'
); do
    port=
    for p in 25 587; do
        [ "$VERBOSE" ] && echo "Testing $m on port $p"
        nc -z $m $p > /dev/null 2>&1 || continue
        port=$p
        break
    done
    if [ ! "$port" ]; then
        [ "$VERBOSE" ] &&
            echo "Unable to connect to $m (ports: 25 587)" >&2
        continue
    fi
    mx=$m
    break
done
if [ ! "$mx" ]; then
    echo "Unable to connect to $domain mail server!" >&2
    exit $FAILURE
fi
export mx port

#
# Contact the mail server and test the recipient address
#
[ "$VERBOSE" ] && echo "Connecting to mail server $mx on port $p"
echo 'eval $env(EXPECT_CMD)' | expect -f- |
    awk '/^(250|550)[ -]/{r=$1}END{exit r!~/^250/}'
retval=$?
if [ $retval -eq $SUCCESS ]; then
    echo "$email exists (mx=$mx:$port)"
else
    echo "$email does not exist (mx=$mx:$port)"
fi
exit $retval

################################################################################
# END
################################################################################
#
# $Copyright: 2015 Devin Teske. All rights reserved. $
#
# $Header$
#
################################################################################