diff --git a/addons/calendar/models/calendar.py b/addons/calendar/models/calendar.py
index c543f5ea830..7245f4943fd 100644
--- a/addons/calendar/models/calendar.py
+++ b/addons/calendar/models/calendar.py
@@ -170,6 +170,7 @@ class Attendee(models.Model):
                 vals = {}
                 if ics_file:
                     vals['attachment_ids'] = [(0, 0, {'name': 'invitation.ics',
+                                                      'mimetype': 'text/calendar',
                                                       'datas_fname': 'invitation.ics',
                                                       'datas': str(ics_file).encode('base64')})]
                 vals['model'] = None  # We don't want to have the mail in the tchatter while in queue!
diff --git a/addons/mail/models/mail_mail.py b/addons/mail/models/mail_mail.py
index ff25c60f04a..3ac2285fab3 100644
--- a/addons/mail/models/mail_mail.py
+++ b/addons/mail/models/mail_mail.py
@@ -270,8 +270,8 @@ class MailMail(models.Model):
                 # load attachment binary data with a separate read(), as prefetching all
                 # `datas` (binary field) could bloat the browse cache, triggerring
                 # soft/hard mem limits with temporary data.
-                attachments = [(a['datas_fname'], base64.b64decode(a['datas']))
-                               for a in mail.attachment_ids.sudo().read(['datas_fname', 'datas'])]
+                attachments = [(a['datas_fname'], base64.b64decode(a['datas']), a['mimetype'])
+                               for a in mail.attachment_ids.sudo().read(['datas_fname', 'datas', 'mimetype'])]
 
                 # specific behavior to customize the send email for notified partners
                 email_list = []
diff --git a/odoo/addons/base/ir/ir_mail_server.py b/odoo/addons/base/ir/ir_mail_server.py
index 37a8126aaac..c061b56f625 100644
--- a/odoo/addons/base/ir/ir_mail_server.py
+++ b/odoo/addons/base/ir/ir_mail_server.py
@@ -355,9 +355,13 @@ class IrMailServer(models.Model):
             msg.attach(email_text_part)
 
         if attachments:
-            for (fname, fcontent) in attachments:
+            for (fname, fcontent, mime) in attachments:
                 filename_rfc2047 = encode_header_param(fname)
-                part = MIMEBase('application', "octet-stream")
+                if mime and '/' in mime:
+                    maintype, subtype = mime.split('/', 1)
+                    part = MIMEBase(maintype, subtype)
+                else:
+                    part = MIMEBase('application', "octet-stream")
 
                 # The default RFC2231 encoding of Message.add_header() works in Thunderbird but not GMail
                 # so we fix it by using RFC2047 encoding for the filename instead.