mac.com is by no means the only ISP to use this practice of more-or-less quietly discarding incoming e-mail based on unclear filtering criteria. It's pretty easy to test for this: if you turn off any filters you have applied yourself and you are still not getting at least several e-mails a week advertising "herbal viagra," "Internet detective kit," "Grow PENIS Grow!," and items at a similar level of encluement, your ISP is probably filtering your e-mail silently.

I could get a whole essay, possibly even a conference paper, out of an analysis of approaches to spam filtering offered by two competing shell-service ISPs. I described some of the elements of this in the panix.* newsgroups over the last six months or so.

I think that Panix is sufficiently transparently operated that I can be confident that there's no secret filtering going on. In contrast, an in-house system administrator I know recently got enough complaints to add a special-case filter to block a repeatedly received obnoxious spam. I've done it myself, and I know other system administrators who do it.

I've now seen and helped maintain the kind of megalomaniac filters Apple has to be running on mac.com and I reject that approach, but if your goal is to minimize user complaints it works quite well for long periods of time.

There is no Service Level Agreement in plain sight on the mac.com web site, and I don't recall that I saw one when I signed up. For me, that's a red flag in itself: you signed up to pay nothing, and in exchange mac.com promised to deliver nothing. The lack of spam told me pretty quickly that Apple was silently filtering e-mail, and my experience with filtering told me there was a good chance non-spam would be rejected. I guess I've been in the business too long to think about how that wouldn't be obvious to people with lives.

There is also an aspect of this which puts some responsibility back on the subscribers: who, in a capitalist society, would think that a free e-mail account with no guarantees of performance is a reasonable instrument for conducting business? Yet some people think it's a reasonable way to do business.

Customers definitely need to make a point of understanding and specifying performance in several respects: maximum time to deliver e-mail to your account; whether or not spam filters are present, and if so what options are available for their control; maximum time your mailbox will be inaccessible to you. It probably isn't possible to get really hard limits on these things yet, but unless customers demand them, it never will be.