Improve efficiency of `NotifyEmail` plugin (#679)

When addressing multiple recipients, use the same session to the SMTP
server as designated with the Apprise URL. In this way, subsequent full
roundtrips will be saved.

As many SMTP servers are employing connection rate limiting, as well as
connection accept delays, this will considerably improve both robustness
and performance.

CONTRIBUTIONS.md

@@ -22,10 +22,11 @@ The contributors have been listed in chronological order:
 * Hitesh Sondhi <hitesh@cropsly.com>
   * Mar 2019 - Added Flock Support
 
-* Andreas Motl <andreas@getkotori.org>
+* Andreas Motl <andreas.motl@panodata.org>
   * Mar 2020 - Fix XMPP Support
   * Oct 2022 - Drop support for Python 2
   * Oct 2022 - Add support for Python 3.11
+  * Oct 2022 - Improve efficiency of NotifyEmail
 
 * Joey Espinosa <@particledecay>
   * Apr 3rd 2022 - Added Ntfy Support

apprise/plugins/NotifyEmail.py

@@ -23,8 +23,10 @@
 # OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 # THE SOFTWARE.
 
+import dataclasses
 import re
 import smtplib
+import typing as t
 from email.mime.text import MIMEText
 from email.mime.application import MIMEApplication
 from email.mime.multipart import MIMEMultipart
@@ -282,6 +284,13 @@ EMAIL_TEMPLATES = (
 )
 
 
+@dataclasses.dataclass
+class EmailMessage:
+    recipient: str
+    to_addrs: t.List[str]
+    body: str
+
+
 class NotifyEmail(NotifyBase):
     """
     A wrapper to Email Notifications
@@ -659,15 +668,14 @@ class NotifyEmail(NotifyBase):
         # Initialize our default from name
         from_name = self.from_name if self.from_name else self.app_desc
 
-        # error tracking (used for function return)
-        has_error = False
-
         if not self.targets:
             # There is no one to email; we're done
             self.logger.warning(
                 'There are no Email recipients to notify')
             return False
 
+        messages: t.List[EmailMessage] = []
+
         # Create a copy of the targets list
         emails = list(self.targets)
         while len(emails):
@@ -778,6 +786,19 @@ class NotifyEmail(NotifyBase):
             if reply_to:
                 base['Reply-To'] = ','.join(reply_to)
 
+            message = EmailMessage(
+                recipient=to_addr,
+                to_addrs=[to_addr] + list(cc) + list(bcc),
+                body=base.as_string())
+            messages.append(message)
+
+        return self.submit(messages)
+
+    def submit(self, messages: t.List[EmailMessage]):
+
+        # error tracking (used for function return)
+        has_error = False
+
         # bind the socket variable to the current namespace
         socket = None
 
@@ -808,22 +829,30 @@ class NotifyEmail(NotifyBase):
                 self.logger.debug('Applying user credentials...')
                 socket.login(self.user, self.password)
 
-                # Send the email
+            # Send the emails
+            for message in messages:
+                try:
                     socket.sendmail(
                         self.from_addr,
-                    [to_addr] + list(cc) + list(bcc),
-                    base.as_string())
+                        message.to_addrs,
+                        message.body)
 
                     self.logger.info(
-                    'Sent Email notification to "{}".'.format(to_addr))
+                        f'Sent Email notification to "{message.recipient}".')
+                except (SocketError, smtplib.SMTPException, RuntimeError) as e:
+                    self.logger.warning(
+                        f'Sending email to "{message.recipient}" failed. '
+                        f'Reason: {e}')
+
+                    # Mark as failure
+                    has_error = True
 
         except (SocketError, smtplib.SMTPException, RuntimeError) as e:
             self.logger.warning(
-                    'A Connection error occurred sending Email '
-                    'notification to {}.'.format(self.smtp_host))
-                self.logger.debug('Socket Exception: %s' % str(e))
+                f'Connection error while submitting email to {self.smtp_host}.'
+                f' Reason: {e}')
 
-                # Mark our failure
+            # Mark as failure
             has_error = True
 
         finally:

requirements.txt

@@ -2,6 +2,7 @@
 certifi
 
 # Application dependencies.
+dataclasses; python_version<"3.7"
 requests
 requests-oauthlib
 click >= 5.0

test/test_plugin_email.py

@@ -538,6 +538,38 @@ def test_plugin_email_smtplib_send_okay(mock_smtplib):
     AttachBase.max_file_size = max_file_size
 
 
+@mock.patch('smtplib.SMTP')
+def test_plugin_email_smtplib_send_multiple_recipients(mock_smtplib):
+    """
+    Verify that NotifyEmail() will use a single SMTP session for submitting
+    multiple emails.
+    """
+
+    # Defaults to HTML
+    obj = Apprise.instantiate(
+        'mailto://user:pass@mail.example.org?'
+        'to=foo@example.net,bar@example.com&'
+        'cc=baz@example.org&bcc=qux@example.org', suppress_exceptions=False)
+    assert isinstance(obj, NotifyEmail)
+
+    assert obj.notify(
+        body='body', title='test', notify_type=NotifyType.INFO) is True
+
+    assert mock_smtplib.mock_calls == [
+        mock.call('mail.example.org', 25, None, timeout=15),
+        mock.call().login('user', 'pass'),
+        mock.call().sendmail(
+            'user@mail.example.org',
+            ['foo@example.net', 'baz@example.org', 'qux@example.org'],
+            mock.ANY),
+        mock.call().sendmail(
+            'user@mail.example.org',
+            ['bar@example.com', 'baz@example.org', 'qux@example.org'],
+            mock.ANY),
+        mock.call().quit(),
+    ]
+
+
 @mock.patch('smtplib.SMTP')
 def test_plugin_email_smtplib_internationalization(mock_smtp):
     """