[Users] Can you tell if an email address is valid without sending an email

Charles Lehner cel at celehner.com
Mon Dec 7 00:56:29 CET 2015

On Sun, 6 Dec 2015 20:26:15 +0100
Ricardo Mones <ricardo at mones.org> wrote:

> On Fri, Dec 04, 2015 at 12:44:20PM -0500, David Niklas wrote:
> > Hello,
> > I was thinking that I wanted to be certain that the email addresses
> > I get from people I spell right and that they are valid, but I
> > can't think of a way to determine this unless I actually send the
> > address an email.  
> You and all the spammers out there. Fortunately address validity is
> defined by the receiving server and not by some arbitrary centralised
> authority.

One way to try to validate an address is to connect to the recipient's
SMTP server as if to send a message and then stop after sending RCPT TO,
and then check the result [1] [2]. There is also an SMTP VRFY
command but it's usually disabled. Some servers will give false
positives or block you as discussed at [1], for spam prevention
reasons. I don't know of any mail client that uses this method for 
verifying addresses. Your best bet is probably to send the message to 
what you think is the correct address and then try another if it 

[1] http://stackoverflow.com/questions/27474/email-smtp-validator
[2] https://github.com/zytzagoo/smtp-validate-email

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