ParserOptionsParameterComplianceMode Property

public RfcComplianceMode ParameterComplianceMode { get; set; }

Property Value

In general, you'll probably want this value to be Loose (the default) as it allows maximum interoperability with existing (broken) mail clients and other mail software such as sloppily written perl scripts (aka spambots).

Tip
Even in Strict mode, the parameter parser is fairly liberal in what it accepts. Setting it to Loose just makes it try harder to deal with garbage input.

Reference