@favoritehooker --
Yeah, as Coldi said, mod development is almost complete at this point for v1.0, and the emails have been complete since April.
They were actually the very first part of the mod we had finished. There was a lot of discussion on the old forum (the one that DineBoo set up; I think you are/were registered there, I remember seeing a similar username) about the contents and we tried to get people to participate as much as we could by recruiting in the Thane thread in the ME1 forums (since BW closed the ME3 character forum).
There may be new mail for Citadel, but if so, I'd say probably only one message. It really depends on if we can make it work in the context of what's already present. We've established a certain timeline with the current emails (which we won't be changing), and since the Citadel content can be played at various points in game, that could make this difficult. As a result it would probably mean that we'd err on the side of one, short note. There may be other content we add, it's still up for discussion
One thing we probably will be doing is the SB Terminal thing. And, in that case we'll be providing instructions, so if users want to write their own contents and put them into the game files, it will be pretty easy. This way, people will be able to customize what their Shepard says to Thane

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There are also a couple other things I wanted to point out, in addition to Coldi's excellent post. This really applies to anyone who might want to provide input and ideas. We love hearing from people. Seriously, so many great ideas for this mod came from engaged discussion. I'm looking at you, especially, LoonySpectre. You lurking here, at all, lol?
First, you'll probably want to wait to shout out any ideas for future content until you play through the mod the first time. In your case, you'll want to see the new lore we have in place for the users of the Email module, and see how the rest of the mod comes together. Probably obvious, but figured I should say it, lol.
Next, make sure you take a look at our objectives when making the mod. These can be seen on the OP of this thread and at the top of the "How does ThaneMOD work" page on the website. All decisions regarding ThaneMOD are made with these objectives in mind.
One thing that became very obvious very quickly when working on this mod, was everyone clearly had their own headcanon about this character. No two players saw Thane's personality exactly the same. In addition, we needed to keep the mod as immersive as possible by staying in the "flavor" of BW. And, we also wanted to avoid establishing canon whenever possible.
When it comes to the emails, specifically, all of this meant that we needed to write in Thane's voice, and provide new/alternate story, but we also needed to retain some...vagueness, for lack of a better term. BW tends to not be overly specific about things, if you've noticed, lol. Much is left up to the imagination.
We had lots of fun and great ideas from people. For emails, we had people float fantastic thoughts about describing Kahje, filling in details about Kolyat or discussing his future, explaining various nuances of drell society, and many more. However, these are things that would fall into the "establishing canon" category, and at this point, they fall into the realm of fan-fiction. This wasn't a road we were willing to go down. We had similar discussions regarding the content we choose to show in the epilogue slides, and again we applied the same rules.
So, this has been a bit of a long-winded post (yikes, sorry), but basically what it comes down to is we've tried to make the new content for Thane, feel like it was in the game originally. As immersive as we can, to appeal to as many players as possible. I don't think we succeeded 100%, just due to certain technical limitations, but I think we did the character justice