Can't send e-mails to g-mail accounts...help!

[church on the sound]

I can't send any e-mail to a @gmail.com account. The error message I receive says that my mail is unauthenticated and suggests that I "set up email authentication for your domain" but I do not know how to do so. Any help would be appreciated!

I'm also confused if this is a roundcube setting or a webmail setting!

Thanks so much everyone!

[Dmitry42]

Roundcube - its just web-based mail client.

You must setup your SMTP server -google about DNS, SPF, DMARK, DKIM, SSL-certs.

What gmail error you see? Copy it here.