social/mass_mailing_partner/views/mailing_contact_view.xml

<?xml version="1.0" encoding="utf-8" ?>
<!-- Copyright 2015 Pedro M. Baeza <pedro.baeza@tecnativa.com>
     Copyright 2015 Antonio Espinosa <antonio.espinosa@tecnativa.com>
     Copyright 2015 Javier Iniesta <javieria@antiun.com>
     Copyright 2016 Antonio Espinosa - <antonio.espinosa@tecnativa.com>
     Copyright 2020 Tecnativa - Manuel Calero
     License AGPL-3.0 or later (http://www.gnu.org/licenses/agpl.html). -->
<odoo>

    <record model="ir.ui.view" id="view_mail_mass_mailing_contact_tree">
            <field name="name">mailing.contact.tree.inherit</field>
            <field name="model">mailing.contact</field>
            <field name="inherit_id" ref="mass_mailing.mailing_contact_view_tree" />
            <field name="arch" type="xml">
                <field name="email" position="after">
                    <field name="partner_id" />
                </field>
            </field>
    </record>

    <record model="ir.ui.view" id="view_mail_mass_mailing_contact_form">
        <field name="name">mailing.contact.form.partner</field>
        <field name="model">mailing.contact</field>
        <field name="inherit_id" ref="mass_mailing.mailing_contact_view_form" />
        <field name="arch" type="xml">
            <xpath expr="//field[@name='email']/.." position="after">
                <field name="partner_id" />
            </xpath>
            <field name="title_id" position="attributes">
                <attribute
                    name="attrs"
                >{'readonly': [('partner_id', '!=', False)]}</attribute>
            </field>
            <field name="email" position="attributes">
                <attribute
                    name="attrs"
                >{'readonly': [('partner_id', '!=', False)]}</attribute>
            </field>
            <field name="name" position="attributes">
                <attribute
                    name="attrs"
                >{'readonly': [('partner_id', '!=', False)]}</attribute>
            </field>
            <field name="company_name" position="attributes">
                <attribute
                    name="attrs"
                >{'readonly': [('partner_id', '!=', False)]}</attribute>
            </field>
            <field name="country_id" position="attributes">
                <attribute
                    name="attrs"
                >{'readonly': [('partner_id', '!=', False)]}</attribute>
            </field>
            <field name="tag_ids" position="attributes">
                <attribute
                    name="attrs"
                >{'readonly': [('partner_id', '!=', False)]}</attribute>
            </field>
        </field>
    </record>

    <record model="ir.ui.view" id="view_mail_mass_mailing_contact_search">
        <field name="name">Add partner search field and group by</field>
        <field name="model">mailing.contact</field>
        <field name="inherit_id" ref="mass_mailing.mailing_contact_view_search" />
        <field name="arch" type="xml">
            <field name="name" position="after">
                <field name="partner_id" />
            </field>
            <filter name="group_create_date" position="after">
                <filter
                    string="Partner"
                    name="group_partner"
                    context="{'group_by': 'partner_id'}"
                />
            </filter>
        </field>
    </record>

</odoo>