Today you cannot buy first class postage form USPS.com online with a tracking number. I found hidden in PayPal’s web site the ability to Buy first class postage online with tracking number. You will need a PayPal account and login for the link to work properly:
WHY A TRACKING NUMBER IS IMPORTANT
The very first requirement after you have received an acceptance on the home you made an offer on is to send in your Deposit, also know as the Earnest Money Deposit. EMD. You will be able to send you personal check directly to the escrow account holder, but to be safe, I recommend sending the letter with a tracking number. If you have a PayPal account, you can print the postage online and receive a free tracking number so you know where your large check is and provide that tracking number to escrow for them to track as well.