Too many failures for the recipient

Too many failures for the recipient

Hello!

I've been testing to send signed mails from my account to my Gmail address. I got two errors that said too ERROR CODE :550, There are multiple Subject 5.7.1 headers.
- My first question is if this is a correct error message for my mails?
I then got a 554 error, Too many failures for the recipient.
- My second question is how I can reset that block?

Best regards 
Kristofer