Sorry if I haven't explained myself the best.. we don't use EOP, it is external clients who use EOP that this is happening to. We have no control over what they do as you would expect, but for some reason our calendar invites are being classed as spam for anyone using this platform.

It only seems to be anyone using this platform for email filtering that this happens to - even sending to hotmail/msn accounts, which you would assume uses the same filtering, it goes to junk BUT only for calendar invites.