Mail Server Parameter for "Expand Public Groups"

We, like other environments, have groups setup without an Internet Address. These groups are for Internal Use only. Unfortunately, Users will send emails to an external email while CCing an Internal Group.

Example:

User sends an email to an external email and CCs the "IT Dept" group. They are CCing that group so those members are aware of the issue. The "IT Dept" contains 4 Members. The external email recipient sees "IT Dept" however they are unable to reply to the email since their email system doesn't know what "IT Dept" is.

I know our user can click the "Expand Public Groups" more option prior to sending the email. This replaces the Internal Group (IT Dept) with all the Members of that group. The external email recipient is now able to reply to all without receiving an error.

Idea:

Give the Server Administrator an option to determine whether the Mail Server can automatically expand Internal Groups if an email contains at least one External Email Address. I am thinking a Yes/No option on a configuration document would work.