congratulatory
adjective /kənˌɡrætʃəˈleɪtəri/
  /kənˈɡrætʃələtɔːri/
- expressing feelings of pleasure about somebody's success or good luck
- a congratulatory message
 
Oxford Collocations DictionaryCongratulatory is used with these nouns:- letter
 - pat
 - telegram
 - …