Collective.dms.mailcontent

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- Use current datetime as encoding datetime [sgeulette]

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- Added internal reference number in Title and in SearchableText [sgeulette]

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- Corrected bad index name [sgeulette]

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- Removed Member from add permission. Must be the default. [sgeulette]

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- Add recipients field for incomingmail [cedricmessiant]
- Add ISendingType behaviour [cedricmessiant]
- Add indexer for in_reply_to field [cedricmessiant]
- Updated testing infra [vincentfretin]
- Make reception date a datetime [cedricmessiant]

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- Manage internal_reference field automatically (no user input needed) [sgeulette]
- Add good proposal value in validation error message [sgeulette]
- Update validateIndexValueUniqueness: skip empty value [sgeulette]
- Use plone.formwidget.datetime [cedricmessiant]
- Allow tasks to be added to mails [fredericpeters]