MailEnable SMTP connector routinely crashes.
The following message is repeated 317 times in
%plesk_dir%\Mail Servers\Mail Enable\Logging\SMTP\SMTP-Debug_xxx_log:
11/17/15 01:16:07 ME-IXXXX: [50D7E7227D6047CFA79462ED4CC7B15F.MAI] Remote server returned a response indicating a temporary failure. Server Response: (452 sorry, too many recipients (#4.5.3)**)
A message with too many recipients.
Delete the message from
%plesk_dir%\Mail Servers\Mail Enable\Queues\SMTP\Outgoing\Messages\ folder