Feature: Add envelope_sender

New EmailMessage attribute `envelope_sender` controls ESP's sender,
sending domain, or return path where supported:

* Mailgun: overrides SENDER_DOMAIN on individual message
  (domain portion only)
* Mailjet: becomes `Sender` API param
* Mandrill: becomes `return_path_domain` API param
  (domain portion only)
* SparkPost: becomes `return_path` API param
* Other ESPs: not believed to be supported

Also support undocumented Django SMTP backend behavior, where envelope
sender is given by `message.from_email` when
`message.extra_headers["From"]` is set. Fixes #91.

anymail/backends/base.py

@@ -9,8 +9,9 @@ from requests.structures import CaseInsensitiveDict
 from ..exceptions import AnymailCancelSend, AnymailError, AnymailUnsupportedFeature, AnymailRecipientsRefused
 from ..message import AnymailStatus
 from ..signals import pre_send, post_send
-from ..utils import (Attachment, UNSET, combine, last, get_anymail_setting, parse_address_list,
-                     force_non_lazy, force_non_lazy_list, force_non_lazy_dict, is_lazy)
+from ..utils import (
+    Attachment, UNSET, combine, last, get_anymail_setting, parse_address_list, parse_single_address,
+    force_non_lazy, force_non_lazy_list, force_non_lazy_dict, is_lazy)
 
 
 class AnymailBaseBackend(BaseEmailBackend):
@@ -230,6 +231,7 @@ class BasePayload(object):
     )
     anymail_message_attrs = (
         # Anymail expando-props
+        ('envelope_sender', last, parse_single_address),
         ('metadata', combine, force_non_lazy_dict),
         ('send_at', last, 'aware_datetime'),
         ('tags', combine, force_non_lazy_list),
@@ -293,6 +295,17 @@ class BasePayload(object):
             # This matches the behavior of Django's EmailMessage.message().
             self.set_reply_to(parse_address_list([reply_to]))
 
+        if 'From' in headers:
+            # If message.extra_headers['From'] is supplied, it should override message.from_email,
+            # but message.from_email should be used as the envelope_sender. See:
+            #   - https://code.djangoproject.com/ticket/9214
+            #   - https://github.com/django/django/blob/1.8/django/core/mail/message.py#L269
+            #   - https://github.com/django/django/blob/1.8/django/core/mail/backends/smtp.py#L118-L123
+            header_from = parse_address_list(headers.pop('From', None))
+            envelope_sender = parse_single_address(self.message.from_email)  # must be single address
+            self.set_from_email_list(header_from)
+            self.set_envelope_sender(envelope_sender)
+
         if headers:
             self.set_extra_headers(headers)
 
@@ -431,6 +444,9 @@ class BasePayload(object):
                                   (self.__class__.__module__, self.__class__.__name__))
 
     # Anymail-specific payload construction
+    def set_envelope_sender(self, email):
+        self.unsupported_feature("envelope_sender")
+
     def set_metadata(self, metadata):
         self.unsupported_feature("metadata")
 

anymail/backends/mailgun.py

@@ -162,6 +162,10 @@ class MailgunPayload(RequestsPayload):
             (field, (name, attachment.content, attachment.mimetype))
         )
 
+    def set_envelope_sender(self, email):
+        # Only the domain is used
+        self.sender_domain = email.domain
+
     def set_metadata(self, metadata):
         for key, value in metadata.items():
             self.data["v:%s" % key] = value

anymail/backends/mailjet.py

@@ -221,6 +221,9 @@ class MailjetPayload(RequestsPayload):
             "content": attachment.b64content
         })
 
+    def set_envelope_sender(self, email):
+        self.data["Sender"] = email.addr_spec  # ??? v3 docs unclear
+
     def set_metadata(self, metadata):
         # Mailjet expects a single string payload
         self.data["Mj-EventPayLoad"] = self.serialize_json(metadata)

anymail/backends/mandrill.py

@@ -139,6 +139,10 @@ class MandrillPayload(RequestsPayload):
             "content": attachment.b64content
         })
 
+    def set_envelope_sender(self, email):
+        # Only the domain is used
+        self.data["message"]["return_path_domain"] = email.domain
+
     def set_metadata(self, metadata):
         self.data["message"]["metadata"] = metadata
 
@@ -268,6 +272,10 @@ class MandrillPayload(RequestsPayload):
         self.deprecation_warning('message.merge_vars', 'message.merge_data')
         self.set_merge_data(merge_vars)
 
+    def set_return_path_domain(self, domain):
+        self.deprecation_warning('message.return_path_domain', 'message.envelope_sender')
+        self.esp_extra.setdefault('message', {})['return_path_domain'] = domain
+
     def set_template_name(self, template_name):
         self.deprecation_warning('message.template_name', 'message.template_id')
         self.set_template_id(template_name)

anymail/backends/sparkpost.py

@@ -172,6 +172,9 @@ class SparkPostPayload(BasePayload):
             'data': attachment.b64content})
 
     # Anymail-specific payload construction
+    def set_envelope_sender(self, email):
+        self.params['return_path'] = email.addr_spec
+
     def set_metadata(self, metadata):
         self.params['metadata'] = metadata
 

anymail/backends/test.py

@@ -74,6 +74,9 @@ class TestPayload(BasePayload):
     def set_from_email(self, email):
         self.params['from'] = email
 
+    def set_envelope_sender(self, email):
+        self.params['envelope_sender'] = email.addr_spec
+
     def set_to(self, emails):
         self.params['to'] = emails
         self.recipient_emails += [email.addr_spec for email in emails]