I’m getting this error when I tried to send an email from webmail:
Unable to perform operation. No free disk space.
Note: Main cPanel account and email account doesn’t reach the quota.
1) This might be the case that your server’s disk space is full which you can verify by firing command df -h through SSH.
2) Check inode usage of your server by firing command df -i through SSH.
3) Check inode usage of that particular cPanel account through cPanel > Statistics section.