Any formatting came from this forum, I have no idea what that might be. I am simply using the default editor here. What was the formatting you saw?
An emoji is a collection on uni codes that are accepted in most systems nowadays, they are built into the OS, I think. They are not images sent from anyone.
Since I am using iPadOS, I can see the ‘self’s’ image you sent in Mail. That is not a “third-party” image, however, even if it was, I cannot block them in iPadOS or any other Apple mobile OS. That’s the main reason I try not to ever read an email on my iPhone or my iPad. Nor does SpamSieve work in that hardware.
Hope that explains why you saw what you did. 
← another emoji. BTW, you can find the Unicode for all emojis via a web search. I recommend using DuckDuckGo. 