USPS has a lot of new restrictions when it comes to international mail delivery.
Apart from the country-specific restrictions and laws, USPS does not currently deliver all letters via the First-Class Mail International service at the moment. According to their support channels, for an item to qualify for First-Class International, it has to meet the following requirements:
- Must weigh 4lb (64oz) or less
- Package value must be under $400
- Minimum height is 3.5"
- Maximum length is 24"
- Minimum length is 6"
- Maximum combined length, height, and width is 36" (42" for rolls/tubes)
So, the main issue you might be facing is the height since letters/envelopes/flats do not meet the current height requirement. The package has to be a soft package or a box to meet the minimum requirements.
First-Class International shipping is available for packages and other options that meet the abovementioned requirements.
If you're attempting to forward a mail item to an international address using USPS and you get the error "First-Class International shipping is unavailable for this item. Please select a different delivery option or carrier." it means your item does not meet the current USPS requirements.
In this case, you'll have the following options:
- Adjust the mail item details and choose a different delivery option from the predefined packages offered by USPS that meet the requirements.
- Use a different carrier or shipping option.
- Forward the item manually.
For more information regarding USPS First-Class International Shipping, please consult the USPS website: USPS: First-Class Mail International.