BTinternet is another ISP who use blocklists which seem to pick up every tiny indiscretion (and often block gmail addresses =:-o)
But I saw a friend's TSOhost mail get bounced the other week. AFAICR, the relevant TSOHost IP block blacklisted was only blacklisted by one organisation, so either M$ use that same blacklist or keep their own. That TSOhost account was I think one of their Cloud accounts. My own email & site is a legacy Cpanel site originally on Evohosting (who were bought up by TSO) and I have not had any problems (touch wood).
Real issue I think is a quick and effective means of saying Oy! this email is genuine. </holdingbreath>