You need to recompile the kernel

I was searching through some old papers this morning and came across a document describing how to set a Linux machine up to retrieve email from freeserve. In amongst the 10 pages (or so) was this gem:

So if you didn't have the dummy interface and didn't have ethernet (fairly common in those modem based days) you needed to recompile the linux kernel to enable it. I sign of how far things have moved since then! It then goes into the gory details of sendmail....