RD is the Receipt Date on when USCIS received your I-485 application.
Email and text notifications can be requested with any forms that you file with USCIS by filling in form G-1145.
And for anyone who missed filing form G-1145, you can always go to
https://egov.uscis.gov/ and create an account for yourself and add the receipt numbers for your cases pending with USCIS and then add email / text notifications for each case. I did the same as I was not aware of G-1145. Today I got both email and text message that case is approved. It will take approx a week for all the process to complete and get the cards in hand.
Also FYI, I have been a silent follower of this forum for about a decade, a major portion of which I had little hope about my PD getting current. But the information and thoughtful insightful discussions and calculations by all the folks here kept me sane until I started seeing some light in 2018 and started posting here.
Please feel free to ask anything related to immigration. There are many here who are always ready to help.
Good Luck