Usually everything in normal paper format (A6 to A3) will be scanned.
All contents of letters that are made of materials other than paper, e.g. SIM cards, CDs, USB sticks, plastic cards, identity cards, badges, etc., cannot be processed. Any such content will be sent to the recipient.
Similarly, letters containing PIN codes, money, tickets, vouchers, cheques, etc. will not be scanned and will be sent to the recipient.