DonGould: ya, I saw the links you posted in google too...? I looked at a few and they looked wrong to me, so I looked up the RFC error messages and not random faq doc written by ISPs (yahoo) who are know to often write wrong stuff in their FAQ's.
Point of note - what you posted wasn't from an RFC either. take a look at RFC1893, and you'll see that there are many and varied responses that fit within a 452. One such response is "Over quota", or "Mailbox full" like you indicate, but in this scenario, it has been munged a little to mean "Too many recipients this hour". See Symantec's explanation of this particular error.
452 has a long history of being abused to mean something different by spam and UCE blocking systems, as it has suitably generic subcodes that largely seem to describe the deferral. Which, I'll point out is what's actually happening. A 4xx code in SMTP ultimately means "no, not now, go away and try later", not "bog off, I'll never accept that" - that's 5xx.
Anyway, OP doesn't care anymore, he came for the soapbox, and got the usual response. so, I don't care anymore either.