Links as found on the OSE download page and NE.
- RHEL/CentOS/Oracle 6: OSE | NE
- RHEL/CentOS/Oracle 7: OSE | NE
- Ubuntu14: OSE | NE
- Ubuntu16: OSE | NE
- Ubuntu18 (beta): OSE | NE
Brando Beaumont runs a private mirror of Zimbra install packages, you can find them here