What is the "default" font for iPad mail program

I was playing around with my new iPad. I was in email. Using yahoo mail but it is a function of email as it is the same for spectrum mail and google mail in the iPad email icon. I changed the font to see how it looked without taking notice of the actual name of the font. There are many to choose from and I simply want to go back. All I can see is "default" for the one I have. I tried opening an old mail to see what it was. (It was "default.")

What was it before I changed it? (To get the original font back.)

Solution 1:

It should be San Francisco, the system typeface in iOS, see Apple Typography guidelines

I tried to check comparing it to similar typefaces both in iPad mail and in TextEdit.

Here's mail. Here's TextEdit.

I took "i"s and "a"s as a confirmation that the default is SF. You can see that the length of the first lines are different, but SF has different tracking depending on the context.

And yes, it doesn't seem to be possible to choose again the default font in iPad mail... I succeeded in getting it back by pasting the text somewhere else (i used the Notes app) and copy-pasting again in mail.