I think Outlook uses the spellchecker from M$ Word. Have a look what version of English your Word spellchecker installation is set to and if it has both US and UK english, delete the US version from the list.
Samsung Galaxy S8 review
1995-2015: How technology has changed the world in 20 years
This poetic animation about monsters is illustrated in a Van Gogh painterly style
Apple predictions 2017
Synology invites you to visit them at Insomnia on 26th – 29th August. Book your tickets now and visit Synology.