[Exim] enhanced mail security question

We are going to setup a shopsystem which
delivers sensitive information (creditcard)
via cgi to exim. Exim then does a local
delivery to a user's mailbox.

Since we use a https connection the cgi
should be no problem. But what is with the
local delivery of exim?

Can I tell my boss the MTA will be no
security risk?

For receiving the mail I thought of
setting up a pop3 server using the
openSSL tools.

Any comments are welcome
--
Torsten