Tumblr 5.4 is soaked in messaging things:

There are now sounds for Tumblr messages: Bloops for notifications, fwips when you’re in the app, and shlings when you’ve got something to say. Turn them on in Settings, turn them up with the volume switch.

Send-a-post is in the share menu (...), which also has a new look.

And you can send things over Facebook Messenger to those friends who get you but don’t really get why you’re “Tumblr famous.”