Prozines used to have long locols in the pulp era, 30 pages or more published in minuscule 6 or 8 pt. type. It was by means of those letters that fans first found each other in the early 1930s, and out of which SF fandom grew. Most magazines printed their correspondents’ mailing addresses, enabling the fans to contact one another directly.
According to one theory, Fourth Fandom (because of paper and other shortages faced by fans during WWII kept the number and frequency of fanzines to a minimum) took place mostly in the lettercolumns of the pulp prozines, mainly Planet Stories, Startling Stories and Thrilling Wonder Stories.
Lettercols have been an important part of fanzines, too, and the art of letterhacking can be found in zines such as Voice of the Imagi-Nation and other dedicated letterzines, as well as many genzines. Sometimes the locs comment on the previous issue, sometimes on random thoughts of the writer, sometimes on what someone else wrote in an earlier lettercol — readers may have extensive, multi-issue conversations with each that may not involve the fanzine’s other contents or the faned at all.
Faneds take varied approaches to assembling a lettercol. Some do not edit the letters at all, even publishing the “Dear Editor” salutations at the top and the “Love and kisses, Joe Fann” closings. Others trim them in minor or major ways.
Some arrange locs by order received, main subject or any other scheme that occurs to them. Donn Brazier, in Title, used to scissor the locs apart into separate paragraphs, sort them and paste in the pieces in topical sections. Faneds may make replies, either within the body of the letter (using typography to distinguish their remarks) or between each letter.