Who pays for postage - company or me?

Hi

I've been working as a freelance media analyst for a couple of years, always for the same company, but for different accounts.
One of my accounts requires me to analyse clippings from newspapers and magazines, which come in hard copy in batches of around 100.
These batches can either be collected from the company's office, or the company sends them to me by post.

The company deducts the postage they have to pay for sending me the batches directly from my invoice.

I can understand that if I send the batches back, that I have to pay for postage.
But how common is it that companies also charge their freelancers for the postage the company pays for sending the work out to the freelancer?

Also, as the company deducts their postage directly from my invoice, I don't have a receipt for that, so I assume that I can't deduct it from my taxes. Is this correct?

As I've only been working for this one company, I don't know how this is handled in other companies. Any information on how your clients charge for postage would be greatly appreciated.

Thank you!