Welcome to the forums,
All the contact info (email, phone, & forms) are on this page:
/about/contact_us.html
For sales you can use this form:
/about/contact_us_form.html or contact
sales@zimbra.com
You can also purchase Zimbra online:
/quote/
If this is just for one customer you probably don't fit into the partners category, but if you do a high volume of reselling Zimbra on a frequent basis see:
/partners/