用PHP获取Plesk邮箱信息？

I have set some mail quota's on email addresses that I manage through Plesk.

However, users are complaining that they are not being informed when their inbox is full or nearly full.

So my idea was to send an email to them when their inbox is about 90% full, so I was wondering if I can retrieve mail account information using PHP?

If not, is there another way of doing this? (I'm not too familiar with console commands)

In this answer I skip the Plesk API altogether, and I assume you either store the properties of the mailboxes in a database, hardcode it, or actually use the Plesk API to retrieve it.

Here is how I retrieve the space used by a mailbox:

function getSpaceUsedByMailBox($username,$password)
{
  // open mailbox
  $mailBox = imap_open('{localhost:110/pop3/novalidate-cert}INBOX',$username,$password);
  // test if successful
  $errors = imap_errors();
  if ($errors === FALSE)
  {
    // get info
    $info = imap_mailboxmsginfo($mailBox);
    // give feedback
    echo "Mailbox of $username contains ".$info->Nmsgs.
         ' messages and is '.$info->Size.' bytes big.';
    // flush notices
    imap_errors();
    imap_alerts();
    // close mailbox
    imap_close($mailBox);
    // return info
    return $info;
  }
  // change this to proper error handling
  echo 'ERROR: '.print_r($errors);
  // return nothing
  return NULL;
}

This is just to give you an idea. You have to adapt it to your coding style.