What is the relationship between Whistl and Mail in the context of the input sentence. Choose an answer from: product/material produced; manufacturer; distributed by; industry; position held; original broadcaster; owned by; founded by; distribution format; headquarters location; stock exchange; currency; parent organization; chief executive officer; director/manager; owner of; operator; member of; employer; chairperson; platform; subsidiary; legal form; publisher; developer; brand; business division; location of formation; creator.

But thanks to the exit of City Link last year, and Whistl closing its letters division more recently, Royal Mail now has a clear run on the UK market, while its GLS operations overseas are also paying off handsomely.

Answer: industry