How do you say thank you professionally?

You say thank you professionally by writing a thank you note or email. In that note or email, you can include phrases such as, "Thank you for your meticulous work," "I truly enjoyed working with you," and "I deeply appreciate you taking the time to help me learn our new software."

Being specific and personal while still professional is key to saying thank you to a colleague. You should also make sure you send your note within a week of the project ending to make sure the recipient knows you appreciate them.