I has set up a secondary zoho email address when I opened the account at the very start of the process but cannot delete it or use is as a user email address.
I have been able to set up an additional secondary email using my gmail account and have been able to delete it without a problem but it will not work on the original secondary email.
To try and solve the issue I tried to remain it but have the same issue.
In both cases I am asked to contact my organization administrator to delete the email address but cannot see any way to achieve this.