From d5502c50ca4434d5a304109cdd3e8d18ba5f612e Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?P=C4=93teris=20Caune?= <cuu508@gmail.com>
Date: Fri, 30 Oct 2020 14:18:38 +0200
Subject: [PATCH] Add retries to the the email sending logic

When sending email using Django's default email
backend (SMTP), and if there is a network issue, the backend
can throw SMTPServerDisconnected.

This commit adds a retry logic which retries sending the
email two times when SMTPServerDisconnected is thrown.
---
 CHANGELOG.md     |  1 +
 hc/lib/emails.py | 25 +++++++++++++++++++------
 2 files changed, 20 insertions(+), 6 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 125a54d6..5b02a0ed 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -12,6 +12,7 @@ All notable changes to this project will be documented in this file.
 - Add support for script's exit status in ping URLs (#429)
 - Improve phone number sanitization: remove spaces and hyphens
 - Change the "Test Integration" behavior for webhooks: don't retry failed requests
+- Add retries to the the email sending logic
 
 ## v1.17.0 - 2020-10-14
 
diff --git a/hc/lib/emails.py b/hc/lib/emails.py
index a05ffd32..d62d82bb 100644
--- a/hc/lib/emails.py
+++ b/hc/lib/emails.py
@@ -1,3 +1,4 @@
+import smtplib
 from threading import Thread
 
 from django.conf import settings
@@ -6,6 +7,8 @@ from django.template.loader import render_to_string as render
 
 
 class EmailThread(Thread):
+    MAX_TRIES = 3
+
     def __init__(self, subject, text, html, to, headers):
         Thread.__init__(self)
         self.subject = subject
@@ -15,12 +18,22 @@ class EmailThread(Thread):
         self.headers = headers
 
     def run(self):
-        msg = EmailMultiAlternatives(
-            self.subject, self.text, to=(self.to,), headers=self.headers
-        )
-
-        msg.attach_alternative(self.html, "text/html")
-        msg.send()
+        for attempt in range(0, self.MAX_TRIES):
+            try:
+                msg = EmailMultiAlternatives(
+                    self.subject, self.text, to=(self.to,), headers=self.headers
+                )
+
+                msg.attach_alternative(self.html, "text/html")
+                msg.send()
+            except smtplib.SMTPServerDisconnected as e:
+                if attempt + 1 == self.MAX_TRIES:
+                    # This was the last attempt and it failed:
+                    # re-raise the exception
+                    raise e
+            else:
+                # There was no exception, break out of the retry loop
+                break
 
 
 def send(name, to, ctx, headers={}):