When using Symantec Mobile Encryption for iOS with Symantec Encryption Management Server 3.3.0 and above you need configure a policy.
Please note that Mobile Encryption for iOS reaches EOS (End of Service) on 31 December 2020 and EOL (End of Life) on 31 March 2021.
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.
Please note:
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).