I prefer - encrypted - e-mail as the way of contact.
For Email details such as my PGP-Key please refer to OLBA-RIPE
To simplify sending me an encrypted message you can use PrivacyBox.
Please mention you contact details in the message text if you expect an answer.
If you like to call me please use +49 231 570 2579
(I will reject anonymous calls to this private landline)
There are some that still use fax these days: +49 231 292730018
(It will end up as email to me anyway, so you might rethink sending me a fax)
And finally you might send me letters full of job offers to the following address:
Olaf Baumert
Bissenkamp 1
D-44135 Dortmund
Germany