Whistl said new customer wins amid an e-commerce boom were driving growth in its UK and international parcels business.
They include Monster Books, Goldstone Books and secondhand book e-tailer Alex the Fat Dawg.
Whistl added that long-term customers including Cotton Traders and Yorkshire Building Society have also renewed contracts for its downstream access mail services.
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It said the growth in parcel customers was being driven by an increase in home delivery as a result of Covid-19 and that it was experiencing a “dramatic growth” in its international business too.
Chief executive Nick Wells said: “We are pleased with the strong growth we are experiencing in our international operations.
“Our unique custom clearance product alongside real-time tracking is proving an increasingly attractive and cost-effective product for international e-commerce customers.”