The email field can be shown in lead or opportunity, the below will hide it from both of them

 <record id="crm_lead_view_form_inherit_hide_email" model="ir.ui.view">

        <field name="name">crm.lead.view.form.inherit.hide.email</field>

        <field name="model">crm.lead</field>

        <field name="priority">15</field>

        <field name="inherit_id" ref="crm.crm_lead_view_form"/>

        <field name="arch" type="xml">

            <!-- to hide email from opportunity !-->

            <xpath expr="//group[@name='opportunity_partner']/label[@for='email_from']" position="attributes">

                <attribute name="attrs">{'invisible': 1}</attribute>

            </xpath>

            <xpath expr="//group[@name='opportunity_partner']/div" position="attributes">

                <attribute name="attrs">{'invisible': 1}</attribute>

            </xpath>

            <!-- to hide email from lead !-->

            <xpath expr="//group[@name='lead_info']/label[@for='email_from_group_lead_info']" position="attributes">

                <attribute name="attrs">{'invisible': 1}</attribute>

            </xpath>

            <xpath expr="//group[@name='lead_info']/div[2]" position="attributes">

                <attribute name="attrs">{'invisible': 1}</attribute>

            </xpath>

        </field>

    </record>