A cPanel account's default email address is showing space usage but the email account doesn't contain email.
On cPanel servers the cPanel account email addresses are linked to the cPanel user's default email address so they can all be managed in one place if needed or desired. Dovecot calculates these linked email accounts space into what is shown as part of the user's quota though. This isn't real usage but is linked usage.
This can be cleared by removing the linked mailboxes.
First, get a list for the user. In this example the user is cptest123 and the domain is cptestacct.com:
doveadm mailbox list -u cptest123
results in this output:
[root@cptestvm ~]# doveadm mailbox list -u cptest123
The two linked mailboxes in this example are
And can be removed by running these commands:
doveadm mailbox delete -u cptest123 -s INBOX.acct1@cptestacct_com
doveadm mailbox delete -u cptest123 -s INBOX.acct2@cptestacct_com
Followed by these commands:
doveadm quota recalc -u cptest123
Note: The linked mailboxes may not be causing this issue, which may be due to the mailbox maildirsize data. Only perform this if the mailbox is using maildir:
/scripts/remove_dovecot_index_files --user <cpanel_username>
/scripts/remove_dovecot_index_files --user cptest123
Followed by this command:
/scripts/generate_maildirsize ---verbose -confirm --allaccounts cptest123