If in doubt about an email, you can do one of two things:

1. With the message open, look toward the top left where the subject line is.  Directly below that should have the name or email address the email is from.  Right below that, there is a grey word and triangle - clicking this will show you some additional details including what email address the message was sent from and who exactly it was addressed to (this is a good way to see who is still using your old @pomfretschool.org address or if the message went out through a group).

If you are still suspicious about the email, then try the second method for more detail:

2. Again with the message open, click the three dots by the reply button and then "Show original" - a new window will pop open with some data points such as the from address (to verify it is actually addressed from an account with that company - clearly not so on this one), something named SPF and another named DKIM (these help identify if that email address came from an authorized server - look for those lines to say "PASS" and be suspicious if they don't).