Now you don't to have worry about your private email exposed when use FLARUM, and replace by Google Mail which have better and good Anti-Spam prevention. For big forum like I had (more than a million posts), spam mail may send by real (human) spammer who successfully login in to your Flarum.
Of course you can set different NO-Reply mail address to avoid your real mail, but this is not good for certain email provider. Your FLARUM mail may set as spam. And this is not good for Server.
And another Good News is your EHLO smtp message header is Google, not your SMTP Banner server. Now, you have FREE and valid Mail and Worry Free Mail SMTP without being rejected by user as spam email. Also Free your money from purchasing service mail like MailGun, Mandrill, SendGrid etc.
Now, try this extension https://discuss.flarum.org/d/20443-mailing-by-kilowhat
Send mail, and voila... Raw Message is Google.
Please use wisely. I don't know How many Google limit the number of mail send everyday. Beware! It will cause your account to suspend etc.