Registered mail? Certified mail?
Exactly. You can steal or divert physical mails as easily as you can intercept "radio" mails. During the early part of WW2, the UK routinely diverted physical mails leaving North America to Bermuda where they were "inspected" before being sent on. It's dead simple if you don't mind reading other people's mail.
Speaking of radio, starting with
MT the x-boat system seems - seems mind you - to use masers which makes interception more - not impossible, just more - difficult.
Those are reasonably secure depending on the nation. I'd think they'd have something similar in the Imperium, and possibly elsewhere.
They do, you're just not doing the math. How much
physical mail can fit on 1 dTon compared to how much
electronic mail? And regular shipping - remember those subsidized merchants and their mail contracts? - are going to carry more physical mail to more places than the x-boats can carry or go to.
People are going to send letters. It will cost a lot, but they'll still send them. Sometimes, sending virtual mail will be good enough.
That could cost literally billions of credits to put in place and maintain. I can't see even a megacorp needing such a system on a widespread and regular basis. It'd simply cost far too much to maintain.
We already know they've got them.
MT's Rebellion Sourcebook says as much. Don't forget that the megacorp courier systems are going to skip over even more worlds than the x-boat system does. Such systems aren't covering 11,000 worlds or even small fraction of that.
Same thing (re: IN jump6 couriers - Whipsnade).
It is the same because we already know they do it too and from the same source.
The movers & shakers have their own couriers and so get the news much faster than the unwashed masses.
It doesn't matter what you or I require. Vector retention is canonical. You never used it and I rarely imposed, but it is canonical.
As for tenders, I'd assume that there are several at a minimum in any system and the number increases as the number of links in the system increase. That allows for maintenance, better coverage of the arrival area, and overlap when a tender is moving a boat to be repaired or replaced, that sort of thing.
It's one per link with maybe one or more in-system for maintenance, crew rotation, and so forth. Anything more is a waste of tenders, manpower, and money.
The arrival area is relatively tiny. Jump's physical accuracy is 3,000km per parsec so a 'boat on a 4 parsec hop is going to arrive in a sphere 12,000km in radius. A one gee tender can cover that volume in a trivial amount of time and, seeing as it's handling one arrival and departure every 24 hours, it has the time.