Apt-get update Problem

Hi

i Have Install a XG 125 and have since than the Problem for update my Linux Server this error become. I check on other System is this Problem a Debian Problem and I find nothing.

I think the Problem is the Proxy of Sophos. I want Exeption create, how do it. Whats is the best way for may Problem .

Ign:2 security.debian.org/debian-security stretch/updates InRelease
Ign:3 http://debian.inode.at/debian stretch InRelease
Hit:4 http://debian.inode.at/debian stretch Release
Get:5 security.debian.org/debian-security stretch/updates Release [92.7 kB]
Ign:6 security.debian.org/debian-security stretch/updates Release.gpg
Ign:8 download.proxmox.com/debian stretch InRelease
Get:9 download.proxmox.com/debian stretch Release [2,170 B]
Ign:10 download.proxmox.com/debian stretch Release.gpg
Reading package lists... Done
E: The repository 'security.debian.org/debian-security stretch/updates Release' is no longer signed.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details.
E: The repository 'download.proxmox.com/debian stretch Release' is no longer signed.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details.