X0306 4 2017-05-01 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 2017-05-01 4 M 0 14500 0 A 51398 D Common Stock 2017-05-01 4 M 0 4937 0 A 56335 D Common Stock 2017-05-01 4 M 0 4937 0 A 61272 D Common Stock 2017-05-01 4 F 0 12721 75.76 D 48551 D Restricted Stock Units 0 2017-05-01 4 A 0 29000 0 A Common Stock 29000 29000 D Restricted Stock Units 0 2017-05-01 4 A 0 15800 0 A Common Stock 15800 15800 D Restricted Stock Units 0 2017-05-01 4 A 0 15800 0 A Common Stock 15800 15800 D Restricted Stock Units 0 2017-05-01 4 M 0 14500 0 D Common Stock 14500 14500 D Restricted Stock Units 0 2017-05-01 4 M 0 4937 0 D Common Stock 4937 10863 D Restricted Stock Units 0 2017-05-01 4 M 0 4937 0 D Common Stock 4937 10863 D Vesting of performance-based RSUs ("PRSUs") earned by the Reporting Person on May 1, 2017 as a result of the Reporting Person having met certain performance criteria. Exempt transaction pursuant to Section 16b-3(e) - payment of exercise price or tax liability by delivering or withholding securities incident to the receipt, exercise or vesting of a security issued in accordance with Rule 16b-3. All of the shares reported as disposed of in this Form 4 were relinquished by the Reporting Person and cancelled by the Issuer in exchange for the Issuer's agreement to pay federal and state tax withholding obligations of the Reporting Person resulting from the vesting of RSUs or PRSUs. The Reporting Person did not sell or otherwise dispose of any of the shares reported on this Form 4 for any reason other than to cover required taxes. Each RSU represents a contingent right to receive 1 share of the Issuer's Common Stock upon settlement for no consideration. Represents PRSUs earned by the Reporting Person on May 1, 2017 as a result of the Reporting Person having met certain performance criteria. The RSUs vest as to 1/2 of the total number of shares on May 1, 2017 and thereafter will vest as to 1/4th of the total number of shares in equal annual installments beginning on March 24, 2018. Shares of the Issuer's common stock will be delivered to the Reporting Person following vesting. The RSUs vest as to 5/16th of the total number of shares on May 1, 2017; 3/16th of the total number of shares on March 29, 2018; and thereafter will vest as to 1/4th of the total number of shares in equal annual installments beginning on March 29, 2019. Shares of the Issuer's common stock will be delivered to the Reporting Person following vesting. /s/ Gary Steele by Michael Yang, Attorney-in-Fact 2017-05-03