MacBook email sending fails with spam error

I am having trouble sending emails on my MacBook. I receive an error message that says:

"Sending the message content to the server failed.

The server response was: Your message has been rejected because you have been detected sending high likelyhood spam.

Select a different outgoing mail server from the list below or click Try Later to leave the message in your Outbox until it can be sent."

It is a business email, so I don't want to use a different server.

Thank you