NO! Don't accept it! If they were serious about the settlement they would send it via us mail.
Send them an email back stating you will only consider a physical settlement (on a piece of paper) send to you via the US postal service. You can even tell them that you would be happy to accept that settlement, but you require it in actual writing first.
Keep copies of those emails for your records. If they were serious about the settlement they should have no problem with sending it in the mail. It sounds fishy that they refuse.
Also you can take the initiative. Write up the agreement they stated in the email. Send them a copy asking them to sign it. Inform them that payment will be made as soon as you have a signed agreement in your hand. Keep a copy of this as well and mail it certified mail RR.
This way it looks like you did everything you could to take care of this and that the company dropped the ball, not you.