The e-mail address postmaster@mydomain.com deleted successfully.
Sorry, you do not have access to the domain mydomain.com
The error message is displayed when you delete an email account of a domain from cPanel >> ‘Email Accounts’ that is either shifted under another users account OR usually happens when a domain is swapped from add-on domain to main domain OR vice-versa. You cannot delete an email account from cPanel, and in this case, you have to manually remove the email account entries for domain from the existing account.
The files you need to remove the entries from are
/home/user/etc/domainname.tld/passwd /home/user/etc/domainname.tld/shadow /home/user/.cpanel/email_accounts.yaml
The directory that need to be removed is
/home/user/mail/mydomain.com
where, ‘user’ is the one under who’s account the email address of ‘mydomain.com’ exist.