Allow SMTP configuration via environment variables

This change allows SMTP configuration via email, but users can
still choose to configure the settings directly in local_settings.py

README.md

@@ -101,6 +101,11 @@ Configurations settings loaded from environment variables:
 | [DB_CONN_MAX_AGE](https://docs.djangoproject.com/en/2.1/ref/settings/#conn-max-age) | `0`
 | DB_SSLMODE | `"prefer"` | PostgreSQL-specific, [details](https://blog.github.com/2018-10-21-october21-incident-report/)
 | DB_TARGET_SESSION_ATTRS | `"read-write"` | PostgreSQL-specific, [details](https://www.postgresql.org/docs/10/static/libpq-connect.html#LIBPQ-CONNECT-TARGET-SESSION-ATTRS)
+| EMAIL_HOST | `""` *(empty string)*
+| EMAIL_PORT | `"587"`
+| EMAIL_HOST_USER | `""` *(empty string)*
+| EMAIL_HOST_PASSWORD | `""` *(empty string)*
+| EMAIL_USE_TLS | `"True"`
 | SITE_ROOT | `"http://localhost:8000"`
 | SITE_NAME | `"Mychecks"`
 | MASTER_BADGE_LABEL | `"Mychecks"`
@@ -175,7 +180,8 @@ DATABASES = {
 ## Sending Emails
 
 healthchecks must be able to send email messages, so it can send out login
-links and alerts to users. Put your SMTP server configuration in
+links and alerts to users. Environment variables can be used to configure
+SMTP settings, or your may put your SMTP server configuration in
 `hc/local_settings.py` like so:
 
 ```python

hc/settings.py

@@ -158,6 +158,13 @@ COMPRESS_CSS_HASHING_METHOD = "content"
 DISCORD_CLIENT_ID = os.getenv("DISCORD_CLIENT_ID")
 DISCORD_CLIENT_SECRET = os.getenv("DISCORD_CLIENT_SECRET")
 
+# Email integration
+EMAIL_HOST = os.getenv("EMAIL_HOST", "")
+EMAIL_PORT = envint("EMAIL_PORT", "587")
+EMAIL_HOST_USER = os.getenv("EMAIL_HOST_USER", "")
+EMAIL_HOST_PASSWORD = os.getenv("EMAIL_HOST_PASSWORD", "")
+EMAIL_USE_TLS = envbool("EMAIL_USE_TLS", "True")
+
 # Slack integration
 SLACK_CLIENT_ID = os.getenv("SLACK_CLIENT_ID")
 SLACK_CLIENT_SECRET = os.getenv("SLACK_CLIENT_SECRET")