The letter is I

Walter Hynson to Anna Ibarra
Antelmo Ibarra to Jerome Ideker
William Ideker to Richard Ilg
Agnes Iliff to Foster Inc
Friesian Inc to C Ingold
Ed Ingold to I Inman
Jeremy Inman to Kyle Irby
M Irby to Patricia Iron
Annabel Irons to Jason Irvin
Kathleen Irvin to Justin Isaacs
Adam Isaacson to John Iske
Ed Iskra to Tex Iverson
Charles Ives to Ann Izard