Red exclamation mark in emails.

Hi all,
I was just testing email from 2 of my servers,
I noticed a red exclamation mark on one of my emails (Just beside the sender name). Can anyone explain what it is about. the screenshot is given in the following link.


The sender may not be verified that means have issues with SPF/DKIM records,

If you’re sending from a server that server IP must be included in the SPF record