Achieving highlighted text effect in Mail on iPhone SE

I have encountered this peculiar format in my Mail where the "Hey" in the bottom text is highlighted in a grey box and it's slightly smaller than the plain text. I am not looking for a way to fix it but I just want to know how could I achieve this effect again without copy pasting so I could make my emails appear more diverse in the future?

I have used this in my previous Iphone SE series and I have forgotten about it's features. Can anyone help me with this?

Thanks.

[Edited by Moderator]

Original Title: Highlighting Format in Mail