EVEN BEFORE Mark Mary entered my life, I got more mail than anyone on the block. The postman told me so, perhaps with a hint of complaint, after routinely squeezing magazines atop school bulletins, junk mail, cosmetics offers, bills and the odd, thoroughly crushed letter.

But now, Mark Mary dwarfs my rightful mail, to say nothing of my female.

Maybe it wouldn't be so bad if he were around to sort it or to explain why he gets a variety that I don't. Most of it isn't junk, but useless just the same: I can't pay for all the fancy management seminars and high-technology publications thrown his way.

This summer, for instance, he was invited to a three-day meeting in New York on international technology transfer. Invited, that is, for $855. American Management Associations was offering this experience "if you're concerned about the future growth and profitability of your company's foreign activities."

I don't even know what Mark's domestic activities are, exactly.

But the Commerce Department seems to. It wants him to subscribe to a research service whereby, for $16 ($4.50 microfiche), he can find out about "Numerically Controlled Orbital-Forging Process." For Christmas I guess I could spring $95 for "Industrial Robots, a Survey of Foreign and Domestic U.S. Patents."

With so much reading to do, let alone corporate responsibility, it's a wonder that Value Line Investment Survey is bidding for Mark's time. Mark doubtless gets ample advice from a team of stockbrokers and accountants.

Perhaps he won't mind if I keep this subscription and one to The Wall Street Journal as a small recompense for his use of my address.

In the beginning, I thought it was all a mistake, that Mark's mail was really mine. Diner's Club disabused me of this folly, however, when with great hoopla it invited Mark Mary to take advantage of financial services that were just right for "your kind of person," or some such.

Captivated, I opened the brochure only to behold a smug, clean-shaven young man in a three-piece suit going through his briefcase in the first-class section of an airplane.

When I fly, New York magazine is about as highbrow as I get. And as for first class, the only time I ever flew it was after I noticed that my seatmate on Alitalia was dead when the movie ended.

Surely, Diner's Club didn't mean me. (More recently, it sent us both applications. They arrived the same day and were thrown out in unison.)

Just to prove it, the next time my name went out on a subscription order, it went as M. Enid Marks. Months passed, and all M. Enid got was Figi's Collection for Cooking catalogue and a request from the National Zoo "to join the wildest club in town."

Meanwhile, Mark, ever the well- rounded type, got pleas from Friends of the Earth and the Sierra Club. He also got come-ons to test-drive a Ford, learn about "giant 8-inch shrimp" from Omni magazine, contribute to a campaign to thrash Jesse Helms in 1984 (I lived in North Carolina for some years; did Mark, too?), and join the fight against handguns.

The fact is, I have come to admire the man -- so obviously successful and kind to animals -- who has sailed into my ZIP Code. So when people ask if I have tried to stem the onslaught of gender-confused mail, I recoil. I was brought up never to open someone else's mail, but why should I cut off someone who adds a little high-tech upward mobility to my life?

I do maintain limits. Any charity asking Mark for money doesn't get a check from me. Why should he get the credit? (This might not be such a concern if IRS targeted its mailings to Mark instead of me.) Partly I hesitate to appropriate his mail for fear of ugly ramifications from a sleight- of-sex: disappointing or disgruntling someone if I, not Mark, arrive to take advantage of an offer.

This is a mistake.

When I was sports editor of my high-school newspaper years ago, I received an invitation to National Football Camp -- you know, to watch workouts, learn finer points of the game and maybe hobnob with visiting greats of yesteryear. I have rued the day my ladylike timidity overcame a puckish sense of adventure and persuaded me to decline on grounds of sexually mistaken identity.

No, indeed! I'll never slink away from another chance to dash sexual preconceptions, let alone strike terror into a Ford dealer's heart as I take a new model out for a spin.

"You're not going to give in and justify their stereotypes" by not accepting the test drive, my boyfriend half-admonished (he was in my good graces then, before he sent a letter addressed . . . to Mark).

No, of course I won't shirk my responsibility. It has nothing to do with cowardice or pass,e notions of femininity, lest the two be confused.

It's just that Mark runs up against the same limitations I do: I open our mail, lay all but the pressing bills and the obvious trash on one side of my desk, and then let time decide whether a subscription, recall notice or test-drive offer, if unexpired, is really worth my attention.

And that's the reason there's no Ford in Mark Mary's future.