Hi,
Make sure that the Form and Reply-to addresses you're using match with your domain. So if your domain is example.com both mail addresses should end with @example.com. Other then that you should make sure that you have a valid SPF record in your dns, preferably in combination with DKIM and DMARC.
You SPF record should contain the ip your hosting server is using to send your mail and if you're using an external smtp provider you should include the ip or ip-range your smtp provider is using. In your case at least +ip4:199.xxx.xxx.xxx should be part of your SPF record. You can ask your smtp provider how to include their SPF into yours.