The emails are forwarded to another mailbox but the forwarding is disabled in Plesk > Domains > example.com > Mail Addresses > [email protected] > the Forwarding tab
sieve: [email protected]: redirect action: forwarded to [email protected]
There is an additional filter in webmail configured.
Log in to webmail
Go to Settings > Filters
Find the filter that can be responsible for the redirect. For example:
Remove the filter by clicking the Delete button