It is most important that you make sure your packaging is correct for the item you are sending, especially when sending old 78s.
For these I would suggest that you place a square of cardboard, (cut slightly larger than the record), between each one, then tape all the way round from top to bottom to hold them tightly together. After this I would put them in a box and use bubble wrap or polystyrene chips to protect them.
Vinyls (LPs and 45s) are fairly resilient and if sent singularly, again, cardboard slightly larger than the disc, tape around the edges this time, and its ready to post. Two or three together are fine like this, but any more, and I would find a box to fit.
Tapes (cassettes and reel to reel) can quite easily be catered for with the current "jiffy bags" available from post offices and stationers.
But whatever you use, make sure they are well protected. I cannot accept any liability for items damaged in transit.
I will try to use the original packaging where possible for the return of the items to you.