PHP Error Logs show:
[29-Mar-2014 21:28:41 UTC] PHP Fatal error: Class 'Horde_Mail_Rfc822_GroupList' not found in /wp-content/plugins/post-by-email/include/Horde/Mail/Rfc822.php on line 308
WP dies on a blank screen after clicking "check now."
The server message is marked read but not imported.
This only seems to happen on messages when the post-by-mail-address is included in a large list of 'undisclosed recipients'
Thanks in advance for your help!