Pitch

Mention to those not logged-in how to follow in Outlook/mail
If they already have a Mastodon account themselves, the message would be more annoying than helpful.

Motivation

(The many) people at organisations where everything is Microsoft, are less likely to follow or try anything that is not offered by Microsoft, or are easily confused by it. They often have no install rights. Helping them set up RSS in Outlook might be a powerful 'foot in the door'.