All ESPs: Unicode header handling #448
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Improve Anymail's normalized EmailAddress object: - Stop using Django's undocumented, deprecated sanitize_address() helper - Add ANYMAIL["IDNA_ENCODER"] setting, defaulting to idna2008 [breaking] - Implement a few useful IDNA_ENCODER presets - Add idna package as direct dependency (already sub-dependency of 'requests') - Add uts46 package optional dependency - Add base backend idna_encode method for subclass use - Subclass EmailAddress from Python's modern email.headerregistry.Address object - Add EmailAddress.as_dict() and formatting options useful for various ESPs - Add utils to apply/reverse RFC 2047 encoded-word and RFC 5322 quoted-string formatting Update each ESP's EmailBackend to use the appropriate EmailAddress and header encodings, based on testing its API's behavior for Unicode characters. Add some ESP-specific unsupported feature errors to prevent particularly problematic Unicode handling: - Brevo: Prevent non-ASCII values in custom headers to avoid raw, 8-bit utf-8 (also affects metadata, which uses a custom header) - Mailgun: Prevent EAI in from_email (API accepts EAI, but generated message is undeliverable) - Scaleway: Prevent EAI in any address field (API accepts EAI, but generated message is undeliverable) Documentation: - Add a new "International email" page in the advanced section, with general details on Unicode handling and the new IDNA_ENCODER setting - Update each ESP's page to indicate whether it handles EAI - Document some other ESP-specific Unicode quirks uncovered during testing Closes #444
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Based on testing each ESP's handling of Unicode in their API, update Anymail's ESP documentation, tests, and (where necessary) EmailBackends to ensure correct handling of non-ASCII characters in email headers.
As part of this work:
IDNA_ENCODERAnymail setting allowing control of IDNA for Unicode domains (IDNs), defaulting to idna2008(Unicode attachment handling will be covered in a separate issue and PR.)