7 years is a long long time friend, still if you think you are feeling like still there is room to enhance the ESA/SMA skills, the best way is to have real time experience in the end customer place, where you will have various scenarios and use cases and dependencies on the end customer infra, as well as experiencing the real time fraud/spam/spoofing/phishing mails coming all your way and the how you manage to play accordingly with the Message tracking logs, fine tuning the policies accordingly etc. . .
I hope this would be much helpful rather than any videos or study materials you can find.
"Experience is the best Master as always "