Dear Olga Nikolaevna, Thank you so much for helping my sister with the application process for US visa,I really appreciate it. Should any of my friends need visas I will definitely refer them to you.
Dear Olga, Thank you and your colleaques for your very professional service in connection with the granting of a UK visa to my friend.
Dear Dr Olga, I am sure we received our visa in record time because of you. My thanks for your professionalism and thoroughness.