diff --git a/addons/mass_mailing/wizard/mail_compose_message.py b/addons/mass_mailing/wizard/mail_compose_message.py
index 8708dd9a098..322057ae616 100644
--- a/addons/mass_mailing/wizard/mail_compose_message.py
+++ b/addons/mass_mailing/wizard/mail_compose_message.py
@@ -62,7 +62,8 @@ class MailComposeMessage(models.TransientModel):
                 if mail_values.get('email_to'):
                     recips = tools.email_split(mail_values['email_to'])
                 else:
-                    recips = tools.email_split(partners_email.get(res_id))
+                    partner_id = (mail_values.get('recipient_ids') or [(False, '')])[0][1]
+                    recips = tools.email_split(partners_email.get(partner_id))
                 mail_to = recips[0].lower() if recips else False
                 if (blacklist and mail_to in blacklist) or (seen_list and mail_to in seen_list):
                     # prevent sending to blocked addresses that were included by mistake
diff --git a/odoo/addons/base/module/module.py b/odoo/addons/base/module/module.py
index cad65d0114e..817ebca1967 100644
--- a/odoo/addons/base/module/module.py
+++ b/odoo/addons/base/module/module.py
@@ -21,6 +21,7 @@ from docutils.core import publish_string
 from docutils.transforms import Transform, writer_aux
 from docutils.writers.html4css1 import Writer
 import lxml.html
+import psycopg2
 
 import odoo
 from odoo import api, fields, models, modules, tools, _
@@ -536,6 +537,14 @@ class Module(models.Model):
 
     @api.multi
     def _button_immediate_function(self, function):
+        try:
+            # This is done because the installation/uninstallation/upgrade can modify a currently
+            # running cron job and prevent it from finishing, and since the ir_cron table is locked
+            # during execution, the lock won't be released until timeout.
+            self._cr.execute("SELECT * FROM ir_cron FOR UPDATE NOWAIT")
+        except psycopg2.OperationalError:
+            raise UserError(_("The server is busy right now, module operations are not possible at"
+                              " this time, please try again later."))
         function(self)
 
         self._cr.commit()