[FIX] mail: avoid crashing for users without email address

addons/mail/models/mail_thread.py

@@ -1929,9 +1929,13 @@ class MailThread(models.AbstractModel):
         self.ensure_one()
         if author_id:
             author = self.env['res.partner'].sudo().browse(author_id)
-        else:
+        elif self.env.user.email:
             author = self.env.user.partner_id
             author_id = author.id
+        else:
+            # the current user has no email address (like the public user)
+            author = self.env.user.browse(SUPERUSER_ID).partner_id
+            author_id = author.id
 
         if not author.email:
             raise exceptions.UserError(_("Unable to log message, please configure the sender's email address."))

addons/mail/wizard/mail_compose_message.py

@@ -63,7 +63,7 @@ class MailComposer(models.TransientModel):
         if 'author_id' not in result:
             result['author_id'] = self.env.user.partner_id.id
             if 'email_from' not in result:
-                result['email_from'] = formataddr((self.env.user.name, self.env.user.email))
+                result['email_from'] = formataddr((self.env.user.name, self.env.user.email or ""))
         else:
             if 'email_from' not in result:
                 author = self.env['res.partner'].browse(result['author_id'])