In over a decade of troubleshooting email related issues, I would say 99% of them are because of disk quota or the server's firewall blocking your IP or setup issues in your email program. They're the 3 main culprits for email problems.
When contacting us on the SolindoHost.com Client area to help with your email issue, we need the following 5 pieces of information -
First things first, let's check that your connecting IP is not being blocked by the server's firewall. This can happen if there are 5 successive unsuccessful login attempts to your cpanel, your WHM, an FTP account or an email account, can trigger the firewall to block that connecting IP, as the server treats that IP as a possible intrusion threat.
What is your connecting IP?
You can see your connecting IP from here » http://whatismyip.com/
Has your domain name in question expired?
If your domain name registration has expired, then your email naturally won't function.
Has your domain name in question resolved to our server?
Another basic question but just ruling out the most obvious causes of email issues. If you've just changed your domain's nameservers, over to our nameservers, then it might take a day or 2 for those nameservers to fully propagate over to our server.
Is there enough disk space assigned to your domain that is having the email issues?
To check go into your WHM » "Quota Modification" and then check that your domain's disk space has not exceeded the disk quota that you set it up with. If it has, then you will need to increase the disk space quota for that domain from there.
Is there enough disk space quota assigned to your email account itself?
This is the amount of disk space that you have created your email account with. So check in your Cpanel » "Mail Management" » "POP Email Accounts" » then click on the Edit Quota link » then add more disk space there.
Please let us know the answer to those 5 questions, and we'll start troubleshooting this email issue with you.