SendGrid does not always correctly provide the sent Message-ID header value
to a tracking webhook's smtp-id field, making it unreliable to use for Anymail's
`message_id`.
Instead, generate a UUID `message_id` for Anymail tracking, and pass it from
send to webhooks in SendGrid custom args as anymail_id.
Webhooks will fall back to smtp-id for compatibility with previously-sent
messages that didn't have an anymail_id custom arg.
Fixes#108
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.
get_api_call_arg had incorrectly returned None if a kwarg was passed
to the mocked function with a False-y value (e.g., [] or {})
get_api_call_json had only considered data param, ignoring json param
requests added a while back
SendGrid requires extra headers and metadata values be strings.
Anymail has always coerced int and float; this treats Python 2's
`long` integer type the same.
Fixes#74
Only real problem is in json serialization tests:
Python 3.6 [changed][1] the json serialization
error message to use the object's class name
rather than its repr. E.g.:
"Decimal('19.99') is not JSON serializable"
becomes:
"Object of type 'Decimal' is not JSON serializable"
Update tests that looked for specific serialization
error message to just look for the word "Decimal"
instead. (Works with all Python versions.)
[1]: https://bugs.python.org/issue26623
SendGrid: update to v3 send API
**SendGrid:** **[possibly-breaking]** Update SendGrid backend to newer Web API v3. This should be a transparent change for most projects. Exceptions: if you use SendGrid username/password auth, esp_extra with "x-smtpapi", or multiple Reply-To addresses, please review the [porting notes](http://anymail.readthedocs.io/en/latest/esps/sendgrid/#sendgrid-v3-upgrade).
Closes#28
