maybe I think this from the gmail EULA covers it:

http://www.google.com/accounts/TOS?hl=en

5.4 You agree that you will not engage in any activity that interferes with or disrupts the Services (or the servers and networks which are connected to the Services).

There has to be some misuse there that spamming "yourself" is breaking when it is an online email account? I havn't checked but what about I would have thought there is something in the agreements that you "check" when you start an account? After all it is using gmail and hotmail's resources (bandwidth, disk space etc) for purposfully receiving spam, which you could argue is verging on a DDOS attack on their servers. (ok the scale may be different but if it wasn't the BBC I expect gmail and hotmail would close those mailboxes pretty quickly if they where filled with thousands of emails in a matter of minutes.