Answer: Configure a response for external senders.
Explanation:
Since Kylee wants to ensure that when a particular client sends her an email while she is on vacation, then the email will be forwarded to a coworker for immediate handling, then she should configure a response for external senders.
It should be noted that the response will not be configured for internal senders as it isn't from a co-worker but rather meant for a client. Therefore, the correct option is A.
