Mail getting bounced with the message “Recipient Mailid is invalid or not exist”

1. Go to the URL http://www.domain name.com/webmail
2. Supply the user name and password

User name : this is the full email id that you have created in the
Cpanelpassword : password of the email that you have created in the cpanel

3.Click on Enter
4. Click on Squirrel mail icon or Horder mail icon
5. Choose Options>>Personal Information>>Check the mailid is given in full format.