I have something like this in my view for a custom module:

 <field name="arch" type="xml">
            <xpath expr="/form/sheet/notebook/page[@string='Contacts']" position="after">
                <page string="External">
                    <iframe src="http://www.example.com?email=__EMAIL_SHOULD_GO_HERE__"></iframe>               
              </page>
        </xpath>
  </field>

where __EMAIL_SHOULD_GO_HERE__ currently is, I need to insert the partner's email. What is the best way to get that value in there?

The only examples I've found use something like:

<field name="email"></field>

Thanks.