Hi Badarac,

We've finally received some info relating to Syntax from our dev team for your question back in Sept. Sorry for the lengthy time it took to get a response.

Stamps.com shold recognize the default shipping status codes used by each shopping cart. So long as a ZenCart customer does not change these defaults, mail classes should be imported.

If the default shipping status codes have been modified in any way, you will have to manually edit the mail class on orders that are pulled into the Stamps.com software.

Let me know if you have any other questions.
Thanks!
Eric
Stamps.com