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
Django allows setting the reply address with either message.reply_to
or message.extra_headers["Reply-To"]. If both are supplied, the extra
headers version takes precedence. (See EmailMessage.message().)
Several Anymail backends had duplicate logic to handle conflicting
properties. Move that logic into the base Payload.
(Also prepares for common handling of extra_headers['From'], later.)
Related changes:
* Use CaseInsensitiveDict for processing extra_headers.
This is potentially a breaking change, but any code that was trying
to send multiple headers differing only in case was likely already
broken. (Email header field names are case-insensitive, per RFC-822.)
* Handle CaseInsensitiveDict in RequestsPayload.serialize_json().
(Several backends had duplicate code for handling this, too.)
* Fixes SparkPost backend, which had been incorrectly treating
message.reply_to and message.extra_headers['Reply-To'] differently.
Within an EmailAddress (previously ParsedEmail object), properties
now match Python 3.6 email.headerregistry.Address naming:
* .email --> .addr_spec
* .name --> .display_name
* .localpart --> .username
(Completes work started in 386668908423d1d4eade90cf7a21a546a1e96514;
this updates remaining uses of old names and removes them.)
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
* **Future breaking change:**
Rename all Anymail backends to just `EmailBackend`,
matching Django's naming convention.
(E.g., switch to "anymail.backends.mailgun.EmailBackend"
rather than "anymail.backends.mailgun.MailgunBackend".)
The old names still work, but will issue a DeprecationWarning
and will be removed in some future release.
(Apologies for this change; the old naming convention was
a holdover from Djrill, and I wanted consistency with
other Django EmailBackends before hitting 1.0.)
Fixes#49.
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
