Currently, an error is generated when attempting to remove a user from followers who have an invalid email address.

Step to produce:

- Install the 'CRM' module without demo data.
- Create a new user 'Test' with the email 'test'
- Create a lead with 'Email' and salesperson 'Test'
- Click on the 'Show Followers' icon (top right corner), and remove 'Test' from Followers.

See Traceback:

```
KeyError: 'email'
  File "odoo/http.py", line 2254, in __call__
    response = request._serve_db()
  File "odoo/http.py", line 1830, in _serve_db
    return self._transactioning(_serve_ir_http, readonly=ro)
  File "odoo/http.py", line 1850, in _transactioning
    return service_model.retrying(func, env=self.env)
  File "odoo/service/model.py", line 134, in retrying
    result = func()
  File "odoo/http.py", line 1828, in _serve_ir_http
    return self._serve_ir_http(rule, args)
  File "odoo/http.py", line 1835, in _serve_ir_http
    response = self.dispatcher.dispatch(rule.endpoint, args)
  File "odoo/http.py", line 2060, in dispatch
    result = self.request.registry['ir.http']._dispatch(endpoint)
  File "odoo/addons/base/models/ir_http.py", line 220, in _dispatch
    result = endpoint(**request.params)
  File "odoo/http.py", line 742, in route_wrapper
    result = endpoint(self, *args, **params_ok)
  File "addons/mail/controllers/thread.py", line 16, in mail_thread_data
    return thread._get_mail_thread_data(request_list)
  File "home/odoo/src/enterprise/saas-17.2/whatsapp/models/mail_thread.py", line 9, in _get_mail_thread_data
    res = super()._get_mail_thread_data(request_list)
  File "addons/mail/models/mail_thread.py", line 4560, in _get_mail_thread_data
    res['suggestedRecipients'] = self._message_get_suggested_recipients()
  File "addons/crm/models/crm_lead.py", line 2007, in _message_get_suggested_recipients
    self._message_add_suggested_recipient(
  File "addons/mail/models/mail_thread.py", line 1836, in _message_add_suggested_recipient
    if email and email in [val['email'] for val in result]:  # already existing email -> skip
  File "addons/mail/models/mail_thread.py", line 1836, in <listcomp>
    if email and email in [val['email'] for val in result]:  # already existing email -> skip
```

The issue occurs when removing user from followers. As a result the system encounter an error because it receives data without an 'email' key at [1].

link[1]: https://github.com/odoo/odoo/blob/5dd1fd84df78e3279c2a949d82199183ddec844a/addons/mail/models/mail_thread.py#L1836

To resolve the issue, use the get() method to retrieve a value from the data to prevent a key error and provide a default value as a False.

sentry-5238024403

---
I confirm I have signed the CLA and read the PR guidelines at www.odoo.com/submit-pr