Hey there,
After reviewing your project description its clear that you have roundcube problem with VestaCP. I know about this issue and why it happens. I can give you a quick fix.
I'm very experienced with System Administration, Linux Administration, SMTP Server Configuration and lot more things.
I'll be happy to do this work for you.
Thanks in advance for giving the opportunity to working with you.
Have a good day.
Best Regards,
Serazum Munir.