totally messed up with Lotus Notes DXL timestamp format... Given is a timestamp of an exported DXL from a Lotus Notes document, which looks like that:
20141104T132939,49+01
Trying to get the format working with DateTime.ParseExact, like:
DateTime.ParseExact(dateStr.Substring(0, 13), "yyyyMMddThhmm", System.Globalization.CultureInfo.InvariantCulture).ToString("dd.MM.yyyy hh:mm");
But with no luck >>> System.FormatException "no valid DateTime format".
Can C# handle the above timestamp as it is?

The problem is your text format - you've used hh which is the 12-hour clock, but you've got a value of 13. You want HH, which is the 24-hour clock. I'd also recommend quoting the T as you just want the literal T character, and also taking the following two characters for the second:
DateTime dateTime = DateTime.ParseExact(
dateStr.Substring(0, 15),
"yyyyMMdd'T'HHmmss",
CultureInfo.InvariantCulture);
I would then suggest keeping it as a DateTime for as long as you can, only converting back to a string where you actually need to display this to a client.
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