Maybe i am in minority (most likely ) but still i would like to voice some things that i see as a big downside with spell "sending".
1) Instant and auto-success
The moment the spell is cast the message can be carried instantly anywhere.
There is no chance for failure either.
2) Performed as a tell
Spell effect is performed as a tell and thus moves role play off screen where noone else could interact with.
3) Free reply.
Myself, i would like to see something different, where sending could create a thing like lightning ball that would state message annonymously in front of character.
This would bring it into interaction with other PCs - one would need to mind where and whom sends it. It would remove free and auto-reply (would require to use own sending).
This change could also make it better scriptable for across server.