The KISS principle needs to be applied to your private email inbox.
Just make a folder called PayPal, and then 2 subfolders within that, ie:
PayPal:
Bought
Sold
As the notifications are received, file them where appropriate.
When it is time to pack and post sold items, just refer to the 'Sold' subfolder for the correct address for each parcel.
When an item is paid for with PayPal, it is the duty of the seller to send to the address noted on the notification of payment to cover themselves and serve the customer.
Many buyers wouldn't make purchases, if the item had to be sent to their address before then being sent on to the person for whom the item was purchased.
That would make the item too expensive, and is the reason PayPal allows 'gift' addresses.
The change of address is a simple step within eBay checkout, and is then reflected on the PayPal payment notification.
However, when I use a 'gift' address - I always send a follow up message to the seller, advising them to make note of the changed of address.