Add Labels/Tags for all mails in any mail account

[lefred]

Feature Request

It would be very useful to be able to use "Labels" (category picker) like for gmail account but for any mail account too (pop3/imap) and store them locally.
Thunderbird provides such functionality (called "Tags").
You can of course search by tag and the color of the tag is also displayed in the message list. For Mailspring-Libre, I would see the tag color as little flag/square color as column.

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[notpushkin]

Nice idea, thank you!

[WillyKaze]

It would be awesome to use IMAP flags for this.
This will enable label synchronization between multiple mail clients:

• Thunderbird use Tags
• Evolution use Labels
• SOGo use Labels

[notpushkin]

@WillyKaze Would be really nice, although need to watch out for servers that don't support arbitrary tags.