bash and telnet to test an email - bash

Question

I'm trying to find out whether an email address is valid.
I've accomplished this by usign telnet, see below
$ telnet mail.example.com 25
Trying 0.0.0.0...
Connected to mail.example.com.
Escape character is '^]'.
220 mail.example.com Mon, 14 Jan 2013 19:01:44 +0000
helo email.com
250 mail.example.com Hello email.com [0.0.0.0]
mail from:blake#email.com
250 OK
rcpt to:gfdgsdfhgsfd#example.com
550 Unknown user
with this 550 request i know that the address is not valid on the mail server... if it was valid i would get a response like the below:
250 2.1.5 OK
How would I automate this in a shell script? so far I have the below
#!/bin/bash
host=`dig mx +short $1 | cut -d ' ' -f2 | head -1`
telnet $host 25
Thanks!

Answer 1

Try doing this :
[[ $4 ]] || {
printf "Usage\n\t$0 <domain> <email> <from_email> <rcpt_email>\n"
exit 1
}
{
sleep 1
echo "helo $2"
sleep 0.5
echo "mail from:<$3>"
sleep 0.5
echo "rcpt to:<$4>"
echo
} | telnet $1 25 |
grep -q "Unknown user" &&
echo "Invalid email" ||
echo "Valid email"
Usage :
./script.sh domain email from_email rcpt_email

Answer 2

You could always enter your commands into a plain text file, line after line, just as if you typed them on the command line. Then you can use something like
cat commands.txt | telnet mail.example.com 25 | grep -i '550 Unknown User'
Since you will probably need to consider this text file as template, (I am assuming you will probably want to parameterize the e-mail address) you may need to insert a call to awk to take the output of 'cat commands.txt' and insert your e-mail address.

Answer 3

variables to change
BODY="open realy smtp test"
SMTP-SRV="server_ip"
SMTP-PORT="25"
RCPT="name#domain"
SRC="name#domain"
then run in bash
/bin/nc ${SMTP-SRV} ${SMTP-PORT} << EOL
ehlo example_domain.com
mail from:${SRC}
RCPT to:${RCPT}
data
From:${SRC}
To:${RCPT}
subject: Telnet test
${BODY}
.
quit
EOL