Haven't done much on this machine yet but when I try to install Postfix it does this to me. I am trying to build an email server for my Linux class.
root@mail:~# sudo apt-get install postfix -y
Reading package lists... Done
Building dependency tree
Reading state information... Done
The following package was automatically installed and is no longer required: python3-netifaces
Use 'sudo apt autoremove' to remove it.
Suggested packages: procmail postfix-mysql postfix-pgsql postfix-ldap postfix-pcre postfix-lmdb postfix-sqlite sasl2-bin dovecot-common resolvconf postfix-cdb postfix-doc
The following NEW packages will be installed: postfix 0 upgraded, 1 newly installed, 0 to remove and 140 not upgraded.
Need to get 1,147 kB of archives.
After this operation, 4,077 kB of additional disk space will be used.
Err:1 http://us.archive.ubuntu.com/ubuntu bionic-updates/main amd64 postfix amd64 3.3.0-1ubuntu0.2 Could not resolve 'us.archive.ubuntu.com' E: Failed to fetch http://us.archive.ubuntu.com/ubuntu/pool/main/p/postfix/postfix_3.3.0-1ubuntu0.2_amd64.deb Could not resolve 'us.archive.ubuntu.com' E: Unable to fetch some archives, maybe run apt-get update or try with --fix-missing?