This is a pretty common question. There are many reporting not getting notices for SA, AIP, or even DM. We didn't see a DM until 2 days before my wife landed. So, my point is: they can be delayed in sending them, or they can be sent to the wrong email address, etc.
One thing you can do, is log into ECAS as your sponsor and check under the "Decision Made" link. If it says they sent you correspondence regarding the decision, then they did actually send it. If it's not there, they have yet to sent that letter to your sponsor.
To answer your follow up question: SA - Sponsorship Approval. This would be correct, and is one of two approvals for inland applications during the first stage. The next is Approval in Principle (AIP).
AIP means you have met the criteria for being a member of the "Family Class" (usually this is where they will ask for more proofs, or the traditional Relationship Interview, before deciding). Once those are completed, your file will move onto the second stage. This is where your Medical, Security, and Criminality checks come into play. Providing the officer(s) are happy with the evidence in the first stage, and have passes for all three additional components, they issue a DM.
They have been requesting QA interviews as of late. They randomly select files to have a quick interview with, for CIC to get the "warm and fuzzies" about the approval(s) issued for the file. They added this because they are trying to process a lot more files then they typically do in the older process.