DKIMValidator
                                
                                
                                
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                        Simple header validation fails with folded value
If the header value is folded and the continuation line contains leading whitespace:
Subject: Subject Subject Subject Subject Subject Subject Subject Subject Subject
 Subject
the simple header canonicalization strips the leading whitespace on the continuation line:
Subject: Subject Subject Subject Subject Subject Subject Subject Subject Subject
Subject 
This leads to an (incorrect) failed validation. According to https://www.rfc-editor.org/rfc/rfc6376#section-3.4.5 the leading whitespace on the continuation line should be preserved.