Why you shouldn't provide a marketplace email address for your recipient.
Marketplace email addresses such as those provided by Amazon or eBay are not suitable for courier use to aid with delivery or customs clearance.
Amazon example: firstname.lastname@example.org
eBay example: email@example.com
If you sell via eBay or Amazon, you may be familiar with these types of email address. The purpose of a marketplace email address is to anonymize a buyer’s real email address with an alias, thus allowing buyers and sellers to communicate via the marketplace messaging platform whilst protecting the privacy of both parties. However, marketplace preference settings allow buyers to decide what type of messages they would like to receive from sellers (if any) and whether they would like to receive copies directly to their private mailboxes. It is therefore possible that messages are either not received or that receipt of a message is only realised once the buyer signs into their marketplace account.
To reduce fraud, spoofing, or transactions taking place outside of the market, some marketplaces will proactively block messages containing links, web addresses or phone numbers and email addresses. This is particularly problematic for couriers as they will often notify importers of duty and tax amounts due for payment via email and will include contact details or a link for payment. If that message is not received and payment not made, your consignment will likely be returned at your cost.
In conclusion, buyer-seller messaging platforms are designed for use between buyers and sellers only. You should obtain and provide your sellers actual email address wherever possible and especially if shipping internationally.