I had a problem when I sent a message to about 20 associates and used BCC. Google apps for business then just marked me as spam. I would get lots of rejected em

I had a problem when I sent a message to about 20 associates and used BCC. Google apps for business then just marked me as spam. I would get lots of rejected email messages. The people I sent to were all people I knew who were attending an event. Just gmail being a dick about BCC. So now I send email through sendgrid from within gmail. Have you tried using an external smtp relay? It's more likely your IP address than your domain that is flagged.