I've been with Seafile for several years now and I love it.
I just found a relatively old plugin for Thunderbird. Although not perfect, it still works wonderfully and I would love to see it followed and maintained as part of the official Seafile project, as it seems the original author stopped working on it.
You can find it here: https://github.com/szimszon/tb-filelink-seafile
All the best.