v3.10

• Added email.recipient_delivery_status field for tracking delivery issues. Thanks @hery733!
• Added FILE_STORAGE option in POST_OFFICE config to specify the storage backend for attachments. Thanks @blag!
• Added Czech translation. Thanks @fdobrovolny!
• Lots of packaging work and converted setup.py to pyproject.toml. Thanks @blag!
• Various admin improvements. Thanks @blag!
• Updated tests and translations. Thanks @samiashi!
• mail.send_many() now returns a list of Email instances. Thanks @chromium7!