Products.easynewsletter

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- Drop Python 2 and Plone < 5.2 support
[MrTango]

- Add marker classes aggregatedContentSlot/aggregatedContent
[MrTango]

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- Improve error handling on email building and sending.
[MrTango]

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- Use min-height for iframe "enl-issue-preview" instead of fixed height in tag.
[MrTango]

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- Improve iframe reziser handling for online view of newsletter issues. Works now better even if JS is broken. Also disable requireJS for the injected JS.
[MrTango]

- fix preview_html method/separat preview window view
[MrTango]

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- Fix image handling in aggregation templates
[MrTango]

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- Fix wrong redirect urls for error redirects in subscribers-upload form
[MrTango]