When using Symantec Mobile Encryption for iOS with Symantec Encryption Management Server 3.3.0 and above you need configure a policy.
Login to the administration console of Encryption Management Server.
Open your Consumer Policy and click on Mobile button and choose the Messaging & Keys sub tab.
Click Enable Mobile Protection to enable secure Send and Reply options (please note: these features require a separate license).
Install Symantec Mobile Encryption for iOS By Symantec https://itunes.apple.com/us/app/symantec-pgp-viewer/id450235714
Enroll with your user from mobile device. Please refer to the User Guide for details.
Mobile Encryption for iOS is able to decrypt PGP-EML, PGP/MIME and PGP Partitioned encoded e-mail.
Replies may be sent either in PGP-EML or PGP Partitioned format, depending on policy and the encoding preferences of the recipient keys.
The app cannot send PGP/MIME encoded messages due to IOS limitations (one of the reasons for this limitation is unavailability of mail headers for modification).