Dear Felix
I am writing to thank your for referring [NAME, ex. Mr. Johnson] to us. [STATE RESULT OF REFERRAL, ex. After demonstrating the Magna flux compressor, Mr. Johnson placed an order with us.] We will be pleased to serve [him/her] in the same capacity we have served you in the past.
[NAME, ex. John], if there is anything I can do for you, call me at XXX-XX-XX and it will be my pleasure to be of any assistance.
Regards
Lydia