further to
preposition /ˈfɜːðə tə/, before vowels  /ˈfɜːðə tu/
  /ˈfɜːrðər tə/, before vowels  /ˈfɜːrðər tu/
(formal)- used in letters, emails, etc. to refer to a previous letter, email, conversation, etc.
- Further to our conversation of last Friday, I would like to book the conference centre for 26 June.