UKDNB obviously has some reservations about the spamming because the last inbox message I got from him (not even a tune) said:
"i appologise if for any reason if i have offended you by sending this message."
On reflection I think inbox messages are worse than privately shared tracks, because at least you can listen to the track and dismiss it.
Whereas I get a lot of:
"I see you follow X, if you like X, come check out my badly produced music that has absolutely no stylistic similarities to X."
The annoying thing is, they seem to get quite a lot of feedback and followers from doing it.