If you want to simplify the opening of multiple CRES messages then there are a couple of options:
1 - If they have Outlook then the Outlook plug-in is one solution. One issue here is although it is "free" you need a Cisco id with an associated service contract to be able to download the plug-in. Also as you have noted you need to be configured for encryption to reply within Outlook, but you can still use the secure reply option if you open the CRES envelope "normally" (in a browser).
2 - If you send them envelopes with medium security then the recipient can "remember" their password in a secure cookie so they entry their password once and then for subsequent envelopes they just click open button. No plug-in is required and any email client can be used. You can set medium security / sensitivity in the encryption profile or in an x-header.
3 - If you send them envelopes with low security (sometimes called "no-authentication") then no password is required and the envelope just opens by clicking the acknowledge button (which replaces the open button). The downside of this is that there is no authentication so the message is encrypted but anyone can open it. Depends on your security requirements as to whether this is acceptable.
In my opinion option 2 would be the best and certainly easiest to implement.
