Well, to answer the question as our esteemed moderator has posed it, there are, as with any on-line special interest group, Web rings that will link you loosly to other maillers' sites. Chain maillers are also quite content to buy and sell advertising from one another, (banner ads and such). And if you become chummy with one--and do stuff distinct from that mailler's stuff--he or she would generally be happy to post a link to you on their Web page for the same consideration.
Source: wiktionary