function StringToWideStringEx(const S: string; CodePage: Word): WideString;
var
  InputLength,
  OutputLength: Integer;
begin
  InputLength := Length(S);
  OutputLength := MultiByteToWideChar(CodePage, 0, PAnsiChar(AnsiString(S)), InputLength, nil, 0);
  SetLength(Result, OutputLength);
  MultiByteToWideChar(CodePage, 0, PAnsiChar(AnsiString(S)), InputLength, PWideChar(Result), OutputLength);
end;

function UTF7ToWideString(const S: string): WideString;
begin
  Result := StringToWideStringEx(S, CP_UTF7);
end;

procedure TForm1.Button1Click(Sender: TObject);
var
I:integer;
SL:TStringList;
M,G:string;
begin
Memo2.Clear;
Memo3.Clear;
SL:=TStringList.Create;
Imap.Connect(True);
try
Imap.ListMailBoxes(SL);
for I := 0 to SL.Count - 1 do
begin
Memo3.Lines.Add(SL.Strings[i]);
Application.ProcessMessages;
M := StringReplace(SL.Strings[i], '&', '+',[rfReplaceAll, rfIgnoreCase]);
G := StringReplace(M, ',', '/',[rfReplaceAll, rfIgnoreCase]);
Memo2.Lines.Add(UTF7ToWideString(G));
end;
finally
SL.Free;
end;
end;