Exchange 2010 SP2
Have a public folder which lets your clients know that their message is received and does not reply to NDR or other kinds of automatically generated messages, such as auto replies etc. to prevent mail loops.
Users will send mail to firstname.lastname@example.org
1. Create auto-reply public folder.
2. Mail enable it.
3. Create Mailbox user which will be responsible for configuring auto-reply on this public folder, you can also assign existing one. I will use a mailbox email@example.com.
4. Grant your mailbox user "Send-as" permissions on auto-reply public folder.
5. Make firstname.lastname@example.org mailbox user Owner of the public folder auto-reply.
6. Create public folder which will receive user mail - queries.
7. On public folder queries properties enable forwarding of mail copies to auto-reply public folder.
8. Using Folder Assistant create auto reply rule for auto-reply public folder which will auto reply to mails sent to email@example.com and then delete the messages.
9. While you're at it also add a rule to delete messages sent to auto-reply (this prevents the piling of useless messages sent automatically to your auto-reply public-folder in cases of NDR's or automatic replies from users).
10. To enable automatic replies for users outside your organization you will need to check the "Allow Automatic Replies" on Remote Domains "Message Format" tab for the Hub Transport role under Organization Configuration in Exchange Management Console.