Determined how to tell if an email address is valid or not without sending one to it.

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#How to check if email is valid 

#Note: this varies on a couple factors, including
#1. sometimes the mailserver will just be mean and not divulge any info
#2. sometimes your ISP might be blocking telnet connections, so you should tether

#this does work with Gmail, amazingly. Zoho too. Seems like others, like block you. 

#figure out their mail servers, by running 
nslookup -q=mx [domain].com

#This will list something like, telnet to it on port 25
#if telnet isn't available can use line below
telnet 25
nc 25

#this will start a session, which is essentially a sending email session
helo hi
#it will respond with a greeting 

mail from: 
#it will respond with OK

rcpt to: 
#it will respond with an error most likely if it doesn't exist, just try an address you know exists

#ends session