X0306 4 2019-06-12 0 0001212458 PROOFPOINT INC PFPT 0001547394 Knight David C/O PROOFPOINT, INC. 892 ROSS DRIVE SUNNYVALE CA 94089 0 1 0 0 EVP Product Mgmnt & Marketing Common Stock 2019-06-12 4 S 0 1260 109.2805 D 15870 D Common Stock 2019-06-12 4 S 0 240 109.9525 D 15630 D This transaction was effected pursuant to a Rule 10b5-1 trading plan previously adopted by the reporting person. Represents the aggregate of sales effected on the same day at different prices. Represents the weighted average sale price. The lowest price at which shares were sold was $108.79 and the highest price at which shares were sold was $109.79. The reporting person undertakes to provide upon request to the staff of the Securities Exchange Commission, the issuer or its stockholders, full information regarding the total number of shares sold at each separate price within the ranges set forth in footnotes (3) and (4) to this Form 4. Represents the weighted average sale price. The lowest price at which shares were sold was $109.81 and the highest price at which shares were sold was $110.07. /s/ David Knight by Michael Yang, Attorney-in-Fact 2019-06-14