Occasionally we need to validate e-mail addresses without send a message to the recipient and wait for answer. For example, we can verify whether an email address given via a simple web form, is not a fake. The principle of such validation involves several steps:
- verification of the existence domain (what is behind the sign)
- verification of the existence MX record for the domain
- connection to the SMTP server according to the MX record
- communication is established according to the SMTP protocol and check the server’s response to the command RcptTo
There are a number of web services, for both manual and automated processing (based on XML-RPC, SOAP, etc.). But not all are free. I have found a service that verifies the email address and returns a clear result of the validation, including a detailed listing of communication with the SMTP server:
The service can be found here: http://convincingemail.com/emailvalidation.aspx
Beware! Not always when the service says that given email does not exist, this is indeed an invalid email!
In many cases, it depends on what SMTP server returns! This may be a temporary problem, blocked traffic SMTP server, etc. In case the service mark email as invalid, it is always necessary to examine in detail the answer mailserver (if any), and find what eas the problem. Conversely, if the validation is successful, we can consider investigated a valid email address.