Dear Mr./Mrs (Name)
It is with mixed feelings that I write. Effective (date), in discussion and agreement with (company) I will be reassigned to the company's newest office in the tourist capital of the country. It's mixed feelings as while my career journey is prolonged and enhanced with this wonderful organisation, managers and staff, I will no longer be able to serve as your Account Manager.
(Company) has given this much thought and by mutual agreement have chosen (name and title) to continue with the high service standards the company is known for. (Name) will be new to your organisation but he has an MBA from Harvard and 10 years solid experience working with similar entities of your size.
He has worked with us for the last 3 years and has expressed delight at the thought of serving you. I can give my personal guarantee that you won't be disappointed. He's meticulous and has a keen eye for creative and workable solutions.
In the next month I will hand over pipeline files to him and would like to set up an introductory meeting for (name) to meet you and your team. Kindly indicate a good time.
I take the opportunity now to express warmest thanks for having allowed me to serve, and a little humor...while I was unable to convice yout to accept my last proposal with such great terms, I enjoyed every minute being Account Manager for your excellent company. In all seriousness, it was a challenging yet very rewarding experience and I am sure our new Account Manager will be exposed to same.
Again, thank you very much and hope to speak soon to arrange a time for the formal handover. Thereafter, I will still be available for meetings but on reassignment, my cell himber or email will be your sure bet. I wish (company) all the very best in their business endeavours. Hope to see you soon!