Logo depicting the hackers emblem in a circle with a highlighted top square



I very much prefer communicating via email and strongly suggest contacting me through my primary account: mail@robertkosten.de.


Please seriously consider encrypting your email with OpenPGP. There are quite straight-forward and free options available for many different Operating Systems, e.g.:

Here is my own Public Key.

If you are already comfortable using OpenPGP then I suggest reading about some of the less-often-mentioned considerations. Deeper understanding is never a bad thing. In the same vein:

  • I have no strong feelings regarding inline vs. PGP/MIME.
  • I do not support S/MIME.
  • I do not currently publish a keysigning policy, inquire directly if necessary.
  • I will gladly explain or debate any part of this.


Please avoid sending me attachments in secret proprietary formats, Microsoft Word (doc and docx) or Microsoft Powerpoint (ppt or pptx) being the most common. Usually plain text will suffice. If fonts and layout really are essential, consider using PDF - Portable Document Format if I’m only supposed to read or ODF - OpenDocument Format if I’m also expected to edit. Both are supported by many free applications, LibreOffice being the prime example.

I’m firmly with Richard Stallman on this one: We Can Put an End to Word Attachments


I’m rather old-school when it comes to email etiquette, please:

  • Do not send HTML email.
  • Do not send big attachments unsolicited.
  • Use To, CC and BCC correctly:
    • To is all those who are directly affected and supposed to read and possibly react. Be aware you are publishing this list to all recipients.
    • CC is all those who may have a general interest to keep apprised, but it’s quite normal for them to completely ignore the email as well. Be aware you are publishing this list to all recipients.
    • BCC is similar to CC but hides the listed names from the other recipients.
    • Most emails should have exactly one address in To and none in CC or BCC.
  • Carefully consider whether to Reply All or not.
  • Do not forward emails without explanation, the original context may not be clear to the recipient and they may not have an idea on what they are supposed to do.
  • Do not request Return Receipts.
  • Unless your email is encrypted, please write an effective subject line.
  • Avoid TOFU - text over, fullquote under of previous messages, only quote those parts you actually wish to respond to. This is also called interleaved posting or inline replying.
  • Reply below the quoted passage. Also called bottom posting.
  • Keep your lines to 72 characters or less.
  • Keep your signature to 4 lines or less, unless required by law. Also called the McQuary limit.
  • Do not write in all-caps, that is considered the equivalent of yelling.
  • Use emoticons sparingly.

Instant and Synchronous communication

If you really have to have ‘just a quick chat’, I’m reachable on XMPP, sometimes called Jabber for historical reasons, at rkosten@robertkosten.de, preferably using OMEMO.

If you already have my mobile phone number, you can also text me via SMS or Signal.

NOTE: I trust both OMEMO and Signal much less than OpenPGP, they are simply the most trustworthy in a field of ‘pragmatic’ solutions where the developers have priorities very different from mine.

Please do not use my phone number to call me unless people are literally, not figuratively, dying.

Actual mail

I love getting real, preferably hand-written, letters, so, if you feel so inclined, for legal reasons my address is in the Imprint at the bottom of this page.


It should be obvious that I avoid proprietary and centralized methods of communication as much as possible. Please do not ask me to join Slack, WhatsApp, Threema, ICQ, Skype, Facebook, Twitter, Google Hangouts, etc. I’m also not particularly inclined to add more Instant Messenging to my life, so the same goes for IRC, Telegam, Matrix, etc.

I do make an exception for recruiters contacting me via LinkedIn or Xing, as I understand the need to use the tools these platforms offer. Still, if you wish to make a real impression: Send me an encrypted email.


This is a personal site. The opinions expressed here are my own and do not necessarily reflect those of my employer.






Robert Kosten
Germersheimer Weg 82
13583 Berlin

© 2019 - 2019 Robert Kosten

Licensed under cc by-nd 4.0