I've signed up to recieve DMARC reports from https://dmarc.postmarkapp.com/
I have setup my email service (Sendgrid) in my DNS so all emails I send are passing DMARC. My email address is using gmail with my own domain name.
However, there are several thousand emails failing, and they appear to be sent from random IP addresses and hosts. What would be causing this? I only send via Sendgrid and 1 or 2 email directly from gmail. I am concerned that a) someone is sending spam from my email address and b) that my email address will be blacklisted and all future emails will go to spam.