Sorted out all other issues (apart from a SSO issue- another thread) . Activesync, autodiscover etc all working- but Outlook Anywhere does not work for Exchange 2007 external mailboxes. It does work for 2013 mailboxes internally and externally- and 2007 mailboxes internally.
Exchange 2013 SP1. Exchange 2007 Sp3 RU10. Legacy namespace is in use and on certificate. Outlook Anywhere IIS Authentication is set to Basic and NTLM on both 2007 and 2013 servers. Outlook Anywhere external client authentication is set to Basic.
Any sugestions what to look at next?