[exim] Do no send auto-replies when sent to alias

How can I setup exim to not send a user's auto-reply when the email was sent to an alias.

Example:
We have an alias called group1 with the following users: user1, user2, and user3.
We also have user4 who is not in the alias.
user2 has an auto-reply set.
If someone sends an email to group1, they should not get user2's auto-reply.
If someone sends an email to group1 and user4, and user4 also has an auto-reply, then only user4's auto-reply should be sent.