eForm just started giving Authentication error and not sending (using SMTP)

Site using evo 1.15 on DreamHost.

I was just contacted by an old client who said their contact form (eForm) has just started giving Authentication errors.

Main mail: Mailer was unable to send mailThe following From address failed: [email protected] : MAIL not accepted from server,530,5.7.1 Authentication required
SMTP server error: 5.7.1 Authentication required
SMTP server error: 5.7.1 Authentication required

Nothing has changed. We have it set to use secure SMTP in the admin settings under Tools -> Configuration -> User. I have tripled checked all the settings and re-saved the password to make sure it was correct.

Can anyone shed some light on why the form that has being working like clockwork would start having errors?

Many Thanks!

Just a guess:

Have you checked if the site has been hacked ? Security issue can be read here

You may also need to read this post in the Forum [ed. note: iusemodx last edited this post 7 years, 10 months ago.]

Dreamhost has reviewed the site and there is no sign of a hack. I'm aware of the security issue and will be recommending any update to my client asap.

Has anyone had eform stop sending for any reason?