Symantec Encryption Desktop and S/MIME takes 30 seconds

We are using PGP Universal 3.3.2 (Build 15704), Symantec Encryption Desktop 10.3.2 MP8 and Outlook 2013.

PGP works like a charm but when a customer sends us S/MIME signed emails it takes 30 seconds till they are displayed and shown as "PGP - S/MIME Signed". Afterwards they are in the local cache and shown instantly till reboot of the client.

Without the Symantec Encryption Desktop running the mails are also shown instantly.

Any ideas where so search the problem?

Regards,
Christian