Dear …
Please allow us to extend our thanks to __(their company name)__ for sponsoring our __(name of event)__this year. Your generosity is greatly appreciated.
I would also like to take this opportunity to express our special thanks to __(name)__ for __(his/her)__ tireless efforts in bringing together the partnering alliance of our two firms. We believe that it is a great match and we thank __(him/her)__ for __(his/her)__ foresight to pursue it. We look forward to bonding together our new business relationship with __(their company name). It is an honor to work with a firm of such professional caliber.
We are glad to hear that __(name)__ will be able to join us for our __(name of event)__ this year. It is our pleasure to have __(him/her)__ join us. Thank you again, for your sponsorship of this event.
Sincerely,