is there any FOSS based webmail and/or IMAP that supports tagging instead of folders?
i use supmua (which inspired notmuch) which like gmail uses tags instead of folders. i could not go back to a folder based system. but i am really missing a webmail interface that works with tags.
* Server-side filters.
* Tags. No, not folders. Many of my emails have 2-3 tags, some have 4-5. I wonder if it can even map to IMAP4; I see a few ways to model it.
* Good deliverability.
* Reasonable spam protection.
* Not hugely expensive. Ideally near-free, or self-hosted.
What are some options?