[Users] [feature request] Add command line input "Run on each change of unread message count"

[mahlamytsike at gmail.com]

Hi !

It can be implemented in two places's:
1. Configuration → Preferences → Mail handling → Receiving → Run command
2. Configuration → Preferences → Plugins → Notification → Command

It is currently possible to implement the situation where Command is triggered when a new message arrives. This provides for example a way to notify the XFCE4 Mail Watcher when a new message has arrived and it can change its icon to "New mail". 

But it is currently difficult to notify XFCE4 Mail Watcher when there are no more new messages and the icon can be changed to "Normal". Claws-mail's Notification plugin, for example, changes its status as soon as there are no new unread emails in the mailbox. Is there a way to run an external command if this state is changed?

Claws Mail 4.1.1
Archlinux

Thanks !