Drupal webform module problem occured send email using webform.
if email does not exist get failure message in inbox
Do we need SMTP
which module we need
and settings(gmail) what we need???
Install the SMTP module

Step 1: Download the SMTP module for Drupal: https://drupal.org/project/smtp

Step 2: Extract to /sites/all/modules

Step 3: Enable the module on Admin - Modules

Step 4 (for Drupal 6 only): you have to install the PHPMailer package from Codeworx Tech., version supported is below 2.2.1. Place it in a directory named "phpmailer" in /sites/all/modules/smtp

For Drupal 7, this is no longer required. The SMTP module for Drupal 7 is shipped with the PHP Mailer. It works out-of-the-box 

Configure with Gmail account

Step 1: Pls go to Admin - Configuration - SMTP Authentication Support

Step 2: On Install Options, please choose On

Step 3: On SMTP server setting, please enter

SMTP server: smtp.gmail.com
SMTP backup server: 
SMTP port: 465
Use encrypted protocol: Use SSL
Step 4: On SMTP Authentication: Enter user name and password of your Gmail account.

Step 5: On Email options: Enter your email from address (could be noreply@yourwebsite.com) and email from name (could be your site name).

Step 6: On Send test email: enter a email to test whether the module is working. Click on Save and go to your inbox to check. If there is an testing email then it is fine. 

If it does not work, you may need to tick on the option "Enable debugging" and send a test email. The responses will be printed so you know more about the problem.

I attach the screenshot of a SMTP configuration.