...I see...now I set the option "Ownertrust" from "full" to "ultimate" and now it says "Absolute trusted signature"
but I got your important point that actually its just trustworthy  if I get the signature from ThomasV personally
Thanks a lot

...I set it to trusted manually - I understand the point you are mentioning - about trust - at one point in the chain you need to trust...which is probably not justified
so if I got you right - the authentication process is ok so far - just wonder why it says not trustworthy even I set it to "trusted" before

Thanks guys so far - I took everything (ThomasV signature, the download itself and the signature of the download) directly from electrum.org but in the end GPG says "Untrusted signature - This signature is not to be trusted"
I must say - I am really not too familiar with this computer stuff - any ideas? 
Thank you

hi, can anybody help me to get the right Electrum's public key I need to enter in the GPG keychain - so that I can verify my electrums download in a second step. What I found so far is from 2017 - its the Thomas Voegtlins public key "0x2bd5824b7f9470e6" - but when I am entering this in the PGP's "lookup for keys" search it doesnt find it.
Thanks a lot
Valentin