Returned Mail API can be queried using either JSON and XML.  Bing processes returned postal mail as it is received from the postal carrier, usually daily. The Returned mail API query should be performed no more than once or twice per day.
To use the Returned Mail API contact Bing Customer Service who can enable it for your account.

JSON

Query current list of returned mail since last reset and without address:

http://easymail.com/publicinterface/returnedmail.json?account=ABC12345

Query current list of returned mail since last reset including address:

http://easymail.com/publicinterface/returnedmail.json?account=ABC12345&address=true

Query current list of returned mail (since last reset) and reset(clear) list:

http://easymail.com/publicinterface/returnedmail.json?_method=PUT&account=ABC12345&reset=true

JSON Response

[{
	"customer_reference": "123456789",
	"epid": "ZZ4RBR76CMF24YPK464CCW4XR6ZZ",
	"idx": 40,
	"dbid": 99999999,
	"reason": "Not Advised By Mail Carrier",
	"returned_posix": 1499832000,
	"returned": "12/07/2017",
	"received": "25/05/2017"
},
{
	"customer_reference": "012345678",
	"epid": "ZZGYFB639R3RMX6T46MQY2FRYYZZ",
	"idx": 63,
	"dbid": 99999999,
	"reason": "Left Address / Unknown",
	"returned_posix": 1499832000,
	"returned": "12/07/2017",
	"received": "15/06/2017"
}]

XML

Query current list of returned mail since last reset and without address:

http://easymail.com/publicinterface/returnedmail.xml?account=ABC12345

Query current list of returned mail since last reset including address:

http://easymail.com/publicinterface/returnedmail.xml?account=ABC12345&address=true

Query current list of returned mail (since last reset) and reset(clear) list:

http://easymail.com/publicinterface/returnedmail.xml?_method=PUT&account=ABC12345&reset=true

XML Response

<ListReturnsResult>
	<ReturnedLetter>
		<CustomerReference>123456789</CustomerReference>
		<Reason>Not Advised By Mail Carrier</Reason>
		<EPID>ZZ4RBR76CMF24YPK464CCW4XR6ZZ</EPID>
		<index>40</index>
		<ReturnedDate>12/07/2017</ReturnedDate>
		<BingDBID>99999999</BingDBID>
		<ReturnedPosix>1499832000</ReturnedPosix>
	</ReturnedLetter>
	<ReturnedLetter>
		<CustomerReference>012345678</CustomerReference>
		<Reason>Left Address / Unknown</Reason>
		<EPID>ZZGYFB639R3RMX6T46MQY2FRYYZZ</EPID>
		<index>63</index>
		<ReturnedDate>12/07/2017</ReturnedDate>
		<BingDBID>99999999</BingDBID>
		<ReturnedPosix>1499832000</ReturnedPosix>
	</ReturnedLetter>
</ListReturnsResult>