Subject: Thank you for your help

Dear [Colleague's Name],

I wanted to take a moment to express my sincere gratitude for your help and support during [project/task name]. Your expertise, guidance and assistance was invaluable and made a real difference in the success of [project/task name].

I greatly appreciate the time and effort that you put into [project/task name], and your willingness to go above and beyond to ensure that everything was done correctly and on time. Your positive attitude and professionalism were an inspiration to me, and I am grateful to have you as a colleague.

Your help was greatly appreciated and I couldn't have done it without you. I feel fortunate to have a colleague like you who is always willing to lend a hand and support when needed.

Thank you once again for all your help, and I look forward to working with you in the future.

Sincerely, [Your Name]