One of the first things you’ll notice after you become engaged is just how much time you spend at the post office. From wedding invitations to thank-you notes, there’s always One More Thing to drop in the mailbox. Birkat Elyon has been working with couples for years, providing them with high-quality cubic zirconia engagement and wedding rings. Here’s a handy list of “when” to send “what.” SAVE-THE-DATES: The rule of…