Exception during GetMessage (unusual UTF-8-Base64 content-type)

[PinkDuck]

ArgumentException exception: System.ArgumentException: 'UTF-8-Base64' is not a supported encoding name. For information on defining a custom encoding, see the documentation for the Encoding.RegisterProvider method.
Parameter name: name
at System.Globalization.EncodingTable.internalGetCodePageFromName(String name)
at System.Globalization.EncodingTable.GetCodePageFromName(String name)
at System.Text.Encoding.GetEncoding(String name)
at OpenPop.Mime.Decode.EncodingFinder.FindEncoding(String characterSet)
at OpenPop.Mime.MessagePart.ParseBodyEncoding(String characterSet)
at OpenPop.Mime.MessagePart..ctor(Byte[] rawBody, MessageHeader headers, IParsingErrorHandler parsingErrorHandler)
at OpenPop.Pop3.Pop3Client.GetMessage(Int32 messageNumber, IParsingErrorHandler parsingErrorHandler)

Email headers inside affected mail item:
Subject: =?UTF-8?B?QVdTIFN1cHBvcnQgVGlja2V0IDIyMDAxNDUgLSBPdGhlciAtIFlvdXIgYWNjb3VudCdzIHNlcnZpY2VzIGFyZSBhYm91dCB0byBiZSBzdXNwZW5kZWQgU3BhbSBTcGFt?=
Content-Transfer-Encoding: base64
Content-Type: text/html; charset="UTF-8-Base64"

Email body is Base64 encoded, subject header uses UTF-8 Base-64 encoding.

Email is spam pretending to be from Amazon.

Email.txt