I'm receiving the following error when I try to send an email using SMTP on my production web server, that holds my wordpress site

the error is

554 5.1.8 Sender Address Blocked

At this moment, there is no DKIM configuration on the server, Is this error related to this?

Or this is a kind of spam block (I'm really not aware about it, so I need to know to take the right actions)

thanks in advance.