X0306 4 2017-11-16 0 0001212458 PROOFPOINT INC PFPT 0001547434 Steele Gary C/O PROOFPOINT, INC. 892 ROSS DRIVE SUNNYVALE CA 94089 1 1 0 0 Chief Executive Officer Common Stock 2017-11-16 4 M 0 40000 3.88 A 88551 D Common Stock 2017-11-16 4 S 0 6253 89.9017 D 82298 D Common Stock 2017-11-16 4 S 0 29241 90.9983 D 53057 D Common Stock 2017-11-16 4 S 0 4506 91.4862 D 48551 D Non-qualified Stock Option (right to buy) 3.88 2017-11-16 4 M 0 40000 0 D 2020-03-09 Common Stock 40000 103015 D The transactions reported on this Form 4 were effected pursuant to a 10b5-1 trading plan adopted by the reporting person on December 7, 2016. Represents the aggregate of sales effected on the same day at different prices. Represents the weighted average sales price per share. The shares sold at prices ranging from $89.40 to $90.24 per share. Full information regarding the number of shares sold at each price shall be provided upon request to the staff of the U.S. Securities and Exchange Commission, the Issuer, or a security holder of the Issuer. Represents the weighted average sales price per share. The shares sold at prices ranging from $90.4001 to $91.39 per share. Full information regarding the number of shares sold at each price shall be provided upon request to the staff of the U.S. Securities and Exchange Commission, the Issuer, or a security holder of the Issuer. Represents the weighted average sales price per share. The shares sold at prices ranging from $91.40 to $91.65 per share. Full information regarding the number of shares sold at each price shall be provided upon request to the staff of the U.S. Securities and Exchange Commission, the Issuer, or a security holder of the Issuer. The stock option is immediately exercisable in full. /s/ Gary Steele by Michael Yang, Attorney-in-Fact 2017-11-20