In sent folder have letters that have an "i", what is this?

[l-il-kitty]

In my sent folder there are several emails that have a circle with an 'i' in
in it. I am wondering what this symbol means?

If any one knows, please let me know, thanks!

 

[Roady [MVP]]

That means that the items contains additional information like for instance
a Read Receipts overview. Double click the item to open it and see the data.

 

[Brian Tillman]

In my sent folder there are several emails that have a circle with an
'i' in in it. I am wondering what this symbol means?

It means that you requested a delivery or read receipt and that you have
received one; i.e., there is recipt information (hence the "i") for that
message.