How did conferences "work" before the e-mail era?
Conferences were organized pretty much as they are now, only slower and with lots more paper.


Conferences would advertise by physically mailing paper fliers to potential authors (primarily past attendees) and perhaps some department chairs.  Postage was a significant portion of the conference budget.  Professional society publications (like Communications of the ACM and SIGACT News) would include several pages of calls for papers with upcoming deadlines.  These calls for papers were typically prepared and sent to publishers/printers about a year in advance of the conference.
Authors would send multiple physical paper copies of each submission by post (or FedEx, or whatever) to the physical address of the program committee chair.  Typically, the author would send one copy for each member of the program committee.  Papers usually had to be received, not merely postmarked, by the submission deadline.  (Hence the probably-not-apocryphal stories of grad students flying to the PC chair's city with a box of last-minute submissions from their home department.)
Submission deadlines were typically about six months before the actual conference date, just as they are now.
The PC chair (or more likely, their secretary and/or students) would collate the received submissions into boxes/binders, which would be physically mailed to each program committee member.  Thus, each PC member would receive a copy of each submitted paper.  Shipping costs were a non-trivial portion of the conference budget.  (Having never been on a committee organized this way, I don't know how review assignments were done.  I assume the now ubiquitous practice of sub-reviewing was very rare.)
A couple of months later, the entire program committee would fly to a central physical location with their submission boxes/binders, to decide which submissions to accept.  Conference budgets sometimes included travel costs for the program committee, but not always.
The PC chair (or more likely, their secretary and/or students) would send a physical letter to each submitting author informing them of the committee's decision about their paper.  Often this was the only feedback from the program committee.  Authors who wanted more information about why a paper was rejected often had to contact one of the committee members directly.
About three months before the conference, authors of accepted papers would physically mail camera-ready copies of their papers to the publisher, after following formatting instructions received by physical mail.  The publisher would duplicate (using an actual camera!) and bind these papers into books, along with front and back matter prepared by the PC chair and also physically mailed to the publisher.
The publisher would ship physical books containing all the camera-ready papers, which would be distributed to the conference attendees.  (Again, shipping costs were a non-trivial portion of the conference budget.)  Faculty attending the conferences would often buy extra books to distribute to their students who could not attend.  Other copies of the same book would be physically mailed to hundreds of university libraries and other subscribers.