How to verify account existence on SMTP server from ASP.NET ?

[darin dimitrov]

Hello,

Is there a way to verify that a particular account exists on SMTP
server before sending email to it in an ASP.NET web application?

 

[M. Zeeshan Mustafa]

Darin,

AFAIK there is no any built in way in ASP.NET,
however it can be achieved by protocol level TCP communication.

Consider this example:
http://www.eggheadcafe.com/articles/20030316.asp

Look at this client server conversation:
c: ehlo myhost
s: 250 ok
c: mail from:[email protected]
s: 250 sender ok
c: rcpt to:[email protected]
s: 250 recipient ok
c: rcpt to:[email protected]
s: 550 invalid address

This way you can detect if an address is valid or invalid.
Be infored that some anti-spam configured MTAs accept
*all* recipient email addresses by default, to fight 'email harvestor'
programs, so your verification may go incorrect

http://en.wikipedia.org/wiki/Mail_transfer_agent

 

[darin dimitrov]

Look at this client server conversation:

c: ehlo myhost
s: 250 ok
c: mail from:[email protected]
s: 250 sender ok
c: rcpt to:[email protected]
s: 250 recipient ok
c: rcpt to:[email protected]
s: 550 invalid address

This way you can detect if an address is valid or invalid.

Zeeshan,

Thank you very much for this post. The TCP conversation you
propose will help me solving my problem.