FAQ.How do I decode correctly an email subject?
Feedback.

Answer: The following code can be used to decode an email subject including several encodings including Base 64.
Example:

Function DecodeEmailHeader(src as string) As String
  
  dim theRegex as Regex
  dim theRegexMatch as RegexMatch
  dim result, infoCharset, encodedPart as string
  dim theStart as integer
  
  if instr(src, "=?") > 0 then
    theRegex = new Regex
    theRegex.Options.Greedy = false
    theRegex.searchPattern = "(.*)=\?(.+)\?(Q|B)\?(.+)\?="
    theRegexMatch = theRegex.search(src)
    while theRegexMatch <> nil
      theStart = theRegexMatch.subExpressionStartB(0) + len(theRegexMatch.subExpressionString(0))
      
      result = result + theRegexMatch.subExpressionString(1)
      infoCharset = theRegexMatch.subExpressionString(2)
      encodedPart = theRegexMatch.subExpressionString(4)
      if theRegexMatch.subExpressionString(3) = "B" then
        encodedPart = DecodeBase64(encodedPart)
      elseif theRegexMatch.subExpressionString(3) = "Q" then
        encodedPart = DecodeQuotedPrintable(encodedPart)
      end if
      if right(result, 1) = " " then
        result = mid(result, 1, len(result)-1)
      end if
      encodedPart = encodedPart.DefineEncoding(GetInternetTextEncoding(infoCharset))
      result = result + encodedPart
      
      theRegex.SearchStartPosition = theStart
      theRegexMatch = theRegex.search()
    wend
    
    result = result + mid(src, theStart+1)
    
  else
    result = src
  end if
  // theRegexMatch = theRegex.search
  
  return result
End Function

Notes: May not look nice depending on the controls used.