Most of the email problems are related to improper configuration of email accounts either in Email clients or in cPanel.
If you have any problem with sending/receiving emails please check following things before sending helpdesk ticket.
1) To send/receive emails Your domain (DNS Nameserver) should be propagated to our servers.
2) Check if your are using correct user name and password.
3) Make sure that Email account has enough disk space to send/receive emails
4) Check if domain on which you are having email issues didn’t exceeded allocated Disk Quota
5) Check if you are having correct email configuration or not. These settings can be found from within your cPanel, under Email Accounts. From there choose the Configuration Information.
6) Make sure that you have enabled “My Server Requires Authentication” checkbox in Email properties >> Server options. You can’t send emails if it’s Disabled.
7) If you are getting SMTP server not responding errors while sending emails:
Many ISP’s block SMTP server port 25 due to spamming issues.
In these instances, when you try to send mail via your hosting account SMTP server you will get timeout or No response Error.
In these cases, you can use port 587.
8) Check if you can login to webmail ( http://www.yourdomain.com/webmail ) and send/receive emails.