You have an Unmanaged Symantec Encryption Desktop (previously PGP Desktop) client which encrypts and decrypts email messages. No outbound email encryption is necessary, but you still want to process and decrypt inbound email.
1) Open Symantec Encryption Desktop Console.
2) Go to 'Edit Policies' and uncheck the option 'Opportunistic encryption (default)'
3) Also uncheck the option 'Require encryption : [PGP] configuration (default)'
4) Click on Done. Now you will be able to send outgoing emails without proxy attempting to encrypt the messages.
PGP Desktop Email
Symantec Encryption Desktop
Symantec Desktop Email Encryption