Support email newsletters (substack, patreon, ghost, etc)

[cscarney]

Support pulling email newsletters from an IMAP inbox. The user specifies a specific sender and syndic creates a feed that shows email messages from that sender.

The most obvious way to do this is to hook into Akonadi. That offers the best integration with Plasma, but has some issues:

• Can't be accessed from flatpak without some questionable permissions or nasty workarounds
• Doesn't work on Android/Gnome
• Only works if using KDE PIM apps for email

Some of that is OK — this isn't a standard/expected feature of an RSS reader, so I don't have a problem saying "here's a plugin that you can install if your mail setup supports it" — but if it can be easily implemented with some cross-platform client library then that would be better.

Implementing and maintaining our own email client to support this feature is probably not a realistic option.

[cscarney]

Another possibility: provide a command-line tool to push an article into a feed. This would allow the email client to send matching messages to syndic using a filter instead of "pulling" them. KMail and Evolution both support filters that pipe messages to a command; Thunderbird could be supported using an add-on.

This is clearly better from a security and compatibility perspective, but I'm not sure that it's possible to provide a decent user experience for this.