Final answer:
The most suitable subject line for an informational email in this context is 'New office policies,' as it is clear, specific, and indicative of the content, thereby engaging the recipient effectively.
Step-by-step explanation:
Choosing the right subject line for an informational email is crucial to ensure that the content is clear to the recipient and encourages them to open and read the email. Considering the information provided, a good subject line is one that indicates exactly what the content of the email will be, which makes it easier for the reader to prioritize and respond to it. Furthermore, the subject line should be specific enough for easy reference at a later date. With that in mind, 'New office policies' would likely be the most suitable subject line, as it is specific, reflects the content of the email if it pertains to new office policies, and is informative enough to prompt the necessary action from the recipients.