Ship200.com is a way to go for all Zencart owners.
there are 2 ways to integrate:
OneByOne
http://blog.ship200.com/onebyone-integration/
and Bulk Processing
http://blog.ship200.com/bulk-processing-integration/
It integrates with Fedex, UPS, Stamps, Endicia from scratch.
and it's FREE!!
http://www.ship200.com/pricing.html
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