Using Plesk API, we running this command returns this error:
<packet version="1.6.3.0">
<mail>
<get_info>
<filter>
<site-id>303</site-id>
</filter>
<mailbox/>
<mailbox-usage/>
</get_info>
</mail>
</packet>
ERROR: Call to a member function hasPlainPassword() on a non-object (AbstractMailName.php:458)
<packet version="1.6.3.0">
<mail>
<get_info>
<filter>
<site-id>303</site-id>
</filter>
<mailbox/>
<mailbox-usage/>
</get_info>
</mail>
</packet>
ERROR: Call to a member function hasPlainPassword() on a non-object (AbstractMailName.php:458)