Unable to send emails to gmail accounts

Thank you. I have added the SPF record that should resolve the issue. If you experience any issues with sending emails, please let us know. 

I have added the SPF record that should resolve the issue. If you experience any issues with sending emails, please let us know. 

We are still having the problem. It appears to mostly happen when replying to a gmail email sent to us. The reply comes back unsendable.

SMTP error from remote mail server after end of data:
    550-5.7.1 [66.96.188.10] Messages missing a valid messageId header are not
    550 5.7.1 accepted. fw14-20020a056214238e00b0049b876cf102si2873966qvb.100 - gsmtp

I struggled with our emails going to Gmail and a few other services. When I just had emails through Homestead, Gmail and a few others almost always would put our emails into junk mail. I was told that Homestead based emails are basically on a no accept spam list. It was extremely frustrating as I'd constantly have to tell people to check their junk mail and always worried about people not receiving our emails. I eventually upgraded to the google based email service through Homestead and it resolved the issue. Go figure, pay money to gmail and they'll allow their customers to receive your emails. I'm not a conspiracy theorist but seems fishy. 

Are you getting this error using Roundcube or an email client like Outlook?

I am using my Homestead email...Roundcube. I can now send an email to a Gmail account, but when they reply, and I try and reply back I get this error message and the email is not sent.