Hi David, I hear what you're saying, and Mr Kandan will have to answer for the Ranga Pen company, but here's my view of the landscape:
(1) I take your point re the dangers of posting when there's no plastic inner lining - but the larger Ranga pens would be monstrously long when posting. I'm not sure they're designed with that concern in mind.
(2) I only have a very small collection of ebonite pens - two Rangas, and a "Triveni" by Fountain Pen Revolution. None of them have problems with nib dryout (which I know is only a part of your concern) - but none of them have a plastic inner liner. As a matter of fact, NONE of my Indian pens, whatever the material used to construct them (plastic, acrylic, metal - I'm talking FPR, Serwex, Camlin, Wality - and Noodler's, which I think is made in India?) have a plastic inner lining - though some of these certainly ARE intended to post. So this seems to be a pretty common practice with these brands of pen. For that matter, I'd be very surprised to find many vintage pens (if any) that incorporated plastic inner linings into their design!
(3) I also have a number of (cheaper) Chinese pens, which DO have plastic inner lining caps - and here's the problem: they're often made of very flimsy plastic, which means that they crack very easily, ESPECIALLY when you try to post the cap on the back of the pen - and when they DO crack, it becomes very difficult both to cap the pen AND to post it thereafter. Granted, a lot of my other (higher quality) pens also have plastic inner caps that are more durable - but they're also (often) somewhat shorter, so that they enclose the nib and prevent the cap being posted too deeply, but don't really do much to shield the material of the cap from brushing against the material of the barrel!
Long story short, the Ranga Pens do NOT have an inner lining made from plastic - like most ebonite pens of yesteryear, for good or for ill, the cap is made pretty much exclusively of ebonite, inside and out.