Attempting to install exim4 via apt fails with the following errors:
E: Failed to fetch https://repo.pureos.net/pureos/pool/main/e/exim4/exim4-config_4.92-8+deb10u1_all.deb 404 Not Found [IP: 138.201.228.45 443] E: Failed to fetch https://repo.pureos.net/pureos/pool/main/e/exim4/exim4-base_4.92-8+deb10u1_amd64.deb 404 Not Found [IP: 138.201.228.45 443] E: Failed to fetch https://repo.pureos.net/pureos/pool/main/e/exim4/exim4-daemon-light_4.92-8+deb10u1_amd64.deb 404 Not Found [IP: 138.201.228.45 443] E: Failed to fetch https://repo.pureos.net/pureos/pool/main/e/exim4/exim4_4.92-8+deb10u1_all.deb 404 Not Found [IP: 138.201.228.45 443] E: Unable to fetch some archives, maybe run apt-get update or try with --fix-missing?
apt reports, for example, that the available version of exim4-base is:
$ apt show exim4-base Package: exim4-base Version: 4.92-8+deb10u1
The .deb file in the repo is in fact:
exim4-base_4.92-8+deb10u3_amd64.deb 28-Sep-2019 23:20 1134852
I wouldn't normally concern myself with exim, but it's a dependency for Emacs...