Is it possible to configure one Mailbox in Exchange 2010 to encrypt the outgoing mails with PGP?
I have the following configuration:
1) External/Public SMTP-Relay (of course relay only for our domains) where all external Mail is sent to and forwarded to the public IP onsite and is also used as a smarthost for outgoing mail. This server runs MailEnable 6.7 Standard.
2) Sophos Astaro ASG110 with UTM 9 as a Firewall and SMTP-Spamfilter
3) Exchange 2010 onsite behind the firewall
I have now one e-Mail address which receives PGP (or S/MIME) encrypted mails and should also be able to send them. I now configured the ASG to decrypt mails received for that one address, but I am stuck with the question how to configure the encryption for outgoing mails.
I can think of the following solutions, but I do not know how to implement them or do not want to go that way and I am also open for other solution:
1) Use some extension for Outlook which does the encryption on the client. I do not want to do this, because more than one person is using this e-Mail address and so I would need to configure it for all of them AND explein them when and how to use it (hard as not very experienced users).
2) Configure Exchange to encrypt outgoing mail from that one mailbox. This would be my prefered solution, but I do not know if this is even possible. The PGP-Key was already created by the ASG.
3) Configure Exchange to use the ASG as Smarthost for that one mailbox as the ASG can also encrypt outgoing e-Mails. Here I face two problems: First I do not know how to tell excahnge to use a different smarthost for one mailbox and second my ASG as a static route configured for SMTP and only forwards external mails to our domains to the internal exchange so it maybe does not even forward the outgoing mails correctly.
4) Use some kind of Mail-Proxy on the Relay.
I appreciate any help on that topic.