As previously announced I’ve been working on per-application settings and a “Do not disturb” mode for xfce4-notifyd, which is Xfce’s notification daemon.
Finally I’ve come to a point where I’m ok with pointing to the code and encouraging people to try it and spot potential issues with it. As both of these features have been long-time requested I hope it’ll 
make quite a few people happy. I know I’ve been quite happy myself since I can use it 
The way that the “known applications” are handled by xfce4-notifyd is that they are remembered once they have sent an application. This means that you can only mute applications which have – at some point since you’ve been running the code from the branch – actually sent notifications. I’ve been previously thinking about trying to collect all potential candidates somehow but this turned out too pesky and personally I think most users will want to mute those applications that send notifications often and those will quickly appear in that (alphabetically sorted) list.
Caveats: Some of this isn’t final – I might still be updating the wording on some of the labels or even some of the functionality might be amended a little, but generally I’m quite pleased with how things are working. Furthermore there may be memory leaks, I just haven’t had the time to really get to that (bugreports and patches are warmly welcomed ;)).
If you have feedback or suggestions please feel free to add some comments to this post or contact me on other communication channels.
So here’s the code: https://git.xfce.org/users/ochosi/xfce4-notifyd/log/?h=private/per_app_settings
Related bugreports: