If you use the x10hosting email as the "From" field but sending it from Mailchimp, it should be fine since it isn't using x10's server itself to send out the bulk emails, however if you were to install a bulk email script on your account and use the x10hosting account server to send out mass emails then it would be against the ToS.
In short, using the email address is fine to do if you are mailing on MailChimp. HOWEVER, you must follow the acceptable use policy:
You may not send any unsolicited e-mail, either in bulk or individually, to any person who has indicated that they do not wish to receive it.
https://x10hosting.com/legal/acceptable-use-policy#Bulk_Email
Using the webmail or a script on your x10hosting account to do the emails will be against the ToS.
You may want to confirm this with a staff member as in terms of Marketing emails, I am not 100% sure if you are using an x10hosting subdomain, but if you are using your own domain, it should be fine.