[#1635] Improve CKAN's SMTP support

Rename config option smtp_server -> smtp.server, add options smtp.starttls,
smtp.user and smtp.password, refactor the email-sending code in
mailer.py to (optionally) support STARTTLS and user and password
authentication. This means CKAN can now send emails using gmail's SMTP
server with a gmail username and password, for example. Sending mail
using a local sendmail process with no STARTTLS, username, or password
should still work as before.

ckan/lib/mailer.py

@@ -36,17 +36,53 @@ def _mail_recipient(recipient_name, recipient_email,
     msg['To'] = Header(recipient, 'utf-8')
     msg['Date'] = Utils.formatdate(time())
     msg['X-Mailer'] = "CKAN %s" % __version__
+
+    # Send the email using Python's smtplib.
+    smtp_connection = smtplib.SMTP()
+    if 'test_smtp_server' in config:
+        # If 'test_smtp_server' is configured we assume we're running tests,
+        # and don't use the smtp.server, starttls, user, password etc. options.
+        smtp_server = config['test_smtp_server']
+        smtp_starttls = False
+        smtp_user = None
+        smtp_password = None
+    else:
+        smtp_server = config.get('smtp.server', 'localhost')
+        smtp_starttls = config.get('smtp.starttls')
+        smtp_user = config.get('smtp.user')
+        smtp_password = config.get('smtp.password')
+    smtp_connection.connect(smtp_server)
     try:
-        server = smtplib.SMTP(
-            config.get('test_smtp_server',
-                       config.get('smtp_server', 'localhost')))
-        #server.set_debuglevel(1)
-        server.sendmail(mail_from, [recipient_email], msg.as_string())
-        server.quit()
-    except Exception, e:
+        #smtp_connection.set_debuglevel(True)
+
+        # Identify ourselves and prompt the server for supported features.
+        smtp_connection.ehlo()
+
+        # If 'smtp.starttls' is on in CKAN config, try to put the SMTP
+        # connection into TLS mode.
+        if smtp_starttls:
+            if smtp_connection.has_extn('STARTTLS'):
+                smtp_connection.starttls()
+                # Re-identify ourselves over TLS connection.
+                smtp_connection.ehlo()
+            else:
+                raise MailerException("SMTP server does not support STARTTLS")
+
+        # If 'smtp.user' is in CKAN config, try to login to SMTP server.
+        if smtp_user:
+            assert smtp_password, ("If smtp.user is configured then "
+                    "smtp.password must be configured as well.")
+            smtp_connection.login(smtp_user, smtp_password)
+
+        smtp_connection.sendmail(mail_from, [recipient_email], msg.as_string())
+        log.info("Sent email to {0}".format(recipient_email))
+
+    except smtplib.SMTPException, e:
         msg = '%r' % e
         log.exception(msg)
         raise MailerException(msg)
+    finally:
+        smtp_connection.quit()
 
 def mail_recipient(recipient_name, recipient_email, subject,
         body, headers={}):