I havent received the official email. It will show in ECAS as "We started processing your application on XX-XX-XXXX" on the PA side. Not all VOs send out official emails
Ecas changed to in process, then shortly after we got an email that said "your application has been sent to the London Visa office" etc, and then within a couple of days a new line in ecas appeared that says "We started processing your application on XX-XX-XXXX"