Whither macOS Server 5.3.6 installer? Until a week ago, I was happily running macOS Server 5.3.6 on High Sierra.
My hard drive failed, resulting in an eternal beachball instead of restarting.  So, I put a clean copy of High Sierra 10.13.6 on an external and rebooted from the new/external startup disk.
Problem:  Neither Server.app, nor the /Library/Server/ directory are present on the clean install.
I need to install Server 5.3.6, the last Server version with support for websites and IMAP mail.
48 hours later I am still searching.
Where can I find a copy of the Server 5.3.6 installer?
Or, should I simply erase the drive and install macOS Sierra [or a given prior macOS version]?
Server is a separate app from the OS, that you download from the Mac App Store. It will be listed in the Purchases of the AppleID that was used to buy it.
You could also copy the app from your backup, and it will create all the necessary folders from scratch. (You may want to copy over the contents of /Library/Server, and other files, to restore your server settings.)