From 2c53344f1f4ac071749b4a9fd394c25d5ec031d9 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Martin=20P=C3=A9pin?= <kerl@wkerl.me>
Date: Wed, 23 Jan 2019 18:18:45 +0100
Subject: [PATCH] Add a helper to handle smtp errors in send_mass_mail

---
 utils/mailutils.py | 54 ++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 54 insertions(+)
 create mode 100644 utils/mailutils.py

diff --git a/utils/mailutils.py b/utils/mailutils.py
new file mode 100644
index 00000000..b52dddf2
--- /dev/null
+++ b/utils/mailutils.py
@@ -0,0 +1,54 @@
+from custommail.shortcuts import send_mass_custom_mail
+from smtplib import SMTPRecipientsRefused
+
+
+def drop_until(predicate, l):
+    """
+    Drop the first elements of the list until we find the first element
+    satisfying the predicate, this element is also dropped.
+    """
+    for i in range(len(l)):
+        if predicate(l[i]):
+            return l[i + 1:]
+    return []
+
+
+def intersects(list1, list2):
+    """ Return True iff there is one element in common in the two lists """
+    return any(x in list2 for x in list1)
+
+
+class SendMassMailRecipientRefused(Exception):
+    pass
+
+
+def send_mass_custom_mail_wrapper(datatuple, *args, **kwargs):
+    """
+    Similar to custommail.shortcuts.send_mass_custom_mail but if an
+    SMTPRecipientsRefused exception is encountered, finish processing the datatuple
+    and only raise at the end of the list.
+    Thus, only the faulty emails won't be sent.
+    """
+    to_be_sent = datatuple
+    in_error = []
+
+    while to_be_sent:
+        try:
+            send_mass_custom_mail(to_be_sent, *args, **kwargs)
+            to_be_sent = []
+        except SMTPRecipientsRefused as exn:
+            # A recipient error has been encountered:
+            # 1. drop already sent emails from the "to be sent" list
+            # 2. move the bogus email from the "to be sent" list to the "in error" list
+            # 3. try to send the remaining emails
+            refused_emails, = exn.args
+
+            def predicate(tuple):
+                __, __, __, recipients = tuple
+                return intersects(refused_emails.keys(), recipients)
+
+            to_be_sent = drop_until(predicate, to_be_sent)
+            in_error.append(refused_emails)
+
+    if in_error:
+        raise SendMassMailRecipientRefused(in_error)