Permissions issue prevents "Set Up Mail Client" from recommending the server's hostname

Symptoms

When using the "Set Up Mail Client" screen in cPanel, the interface recommends using the server's hostname instead of the appropriate mail subdomain.

Description

This issue can occur if there are incorrect permissions on a domain's "TLS" folder at the following path:

/var/cpanel/ssl/domain_tls/$domain/

Workaround

If you access the server through SSH as the root user, the following command will walk through the domain_tls directory and set the permissions correctly for all domains:

find /var/cpanel/ssl/domain_tls -type d -not -perm 755 -exec chmod -v 755 {} \;

Additional Information

Why does Set Up Mail Client recommend the server's hostname?