Dear Ann Landers,
A social craze called Mixed Mates has hit town. The invitation we received yesterday read: "You are cordially invited for cocktails and dinner at Bill and Mary X's home on January 25. But you can't come with your husband. He must escort someone else's wife. You will not know the identity of your escort until he arrives. Your husband will soon receive a phone call assigning a date. But it must be kept a deep, dark secret. Of course you will be taken home by the man who brought you. R.S.V.P." I don't want to be a wet firecracker, but the whole idea offends me. My husband says it's novel and should be fun. What would we tell our teen-age children about such a party? Help, please.--Fraidy Cat

Dear Ann Landers,
I am a postal clerk, and every day, I see many cards, letters and packages sent to our mail recovery center (formerly known as the dead letter branch) because people do not put return addresses on the items they mail. I find it disturbing when mail that is undeliverable cannot be returned to the senders to let them know it didn't reach its destination. Think of the thank you notes, love letters, invitations and condolence cards that never got delivered because of illegible addresses. And imagine the hard feelings, disappointment, misunderstandings and broken relationships that resulted because senders didn't take the time to write their return addresses. When there is no acknowledgment of having received the gift, the sender assumes the recipient has poor manners. This problem could be remedied so easily. Return address labels are inexpensive, and it takes only a minute to affix them. Please, Ann, do your readers and the Postal Service a favor by printing this letter. It really IS important. -- Concerned Postal Clerk in N. Dakota

Dear N. Dakota,
I know a little something about mail and can sympathize with you. I hope your letter produces the desired results. Please, dear readers, pay attention to what this postal clerk is saying. It takes just a minute to print your return address in the upper left corner of the envelope or package or slap on the sticker. DO IT!

Dear Ann Landers,
Our 16-year-old son recently admitted that he is having sex with his girlfriend, "Evie." It's not as if we have never discussed sex. We have had long talks with him about it and discouraged premarital intimacy. He seemed to understand the dangers, but apparently, that didn't stop him. Evie's parents are divorced, but we are friends with both of them. I think the girl should tell her parents that she is having sex so they can advise her and help her choose an appropriate method of birth control. Our son says he is using condoms, but I know they are not always 100 percent reliable. Both of these kids want to go to college, and we are concerned that an unplanned pregnancy could destroy their lives. I don't know how to get Evie to tell her parents. Her mother is a very understanding woman, so this ought not be a problem. Should I let my son know that if Evie doesn't tell her folks, I will? My husband says it is none of our business, but I say what happens to our teenage son definitely IS our business. Please advise me. -- Upset in Cape Coral, Fla.

Dear Cape Coral,
Do NOT tell the girl's parents that their daughter is having sex with your son. The young couple would consider it a betrayal, and it could poison their relationship with you for all time. It is up to Evie to tell her parents, if she chooses to do so. Although your son is demonstrating responsibility by using condoms, he should know that the failure rate for condoms is about 17 percent. A pregnancy for these two would be disastrous. Don't count on a frank discussion to change their behavior, however. Experts tell us that once teenagers become sexually active, they rarely stop. Since your son has told you what is going on, urge him to insist that the girl tell her folks so she can see a gynecologist on a regular basis. It is important that she stay healthy and informed. Some visits with the school counselor would be very helpful. I recommend it.

Dear Ann Landers,
I have never cheated on my wife and am absolutely certain that I never will. We have been married for five wonderful years, and our marriage is rock solid. Here's the problem: About a year ago, during a moment of passion, I happened to call out the name of my wife's best friend, "Annabelle." You can imagine my wife's reaction. Annabelle is single, in her early 20s and good-looking, and she has a terrific figure. She moved out of town three years ago. I made it clear to my wife that nothing ever went on between Annabelle and me and that calling her name was just part of a harmless fantasy. I tried to explain that fantasies are normal and I have no intention of acting them out. My wife accepted this explanation, and things seemed to be going well. Now comes the hard part. Annabelle visits us once a year and stays for a week. Her visit is coming up soon, and my wife has started to turn very cold. In fact, she's downright hostile. I know she is afraid I will be attracted to Annabelle and feels threatened. What can I do to reassure her and get things back on track? -- Faithful in Denver

Dear Denver,
Since you have had sexual fantasies about Annabelle, your wife has some justification for feeling a bit threatened. Start immediately to line up some attractive men for Annabelle to go out with when she is visiting you. Make sure you are never alone with your guest, and most importantly, concentrate on finding a substitute fantasy woman. (Any star of stage or screen will do.) And be especially affectionate to your wife in Annabelle's presence. She will appreciate it.

Dear Ann Landers,
Two years ago, I was a married woman who became involved with a married man at work. At first, it was just flirting, but before long, we knew we were in love. It was exciting and wonderful. We finally decided to divorce our spouses and get married. What do I have today? My two children, who were once happy and well-adjusted, are now in therapy. I also have huge legal bills. My in-laws despise me because they see their grandchildren only twice a year. I have a husband who sits in a chair at night drinking beer and smoking cigarettes while I cook, clean and fold laundry. I wish I had used the effort I spent trying to hide my affair and put it to work saving my first marriage. I would have been a lot happier. Please print my letter so other married women will think before they start fooling around. -- Smart Too Late

Dear Smart,
I wonder how many married women (and men) who are flirting or fooling around in the workplace will see themselves in your letter. I would not be surprised if your words nipped some of those romances in the bud. Thanks for all the marriages you may have saved today. As for yours, I suggest counseling. If the couch potato won't go with you, go alone.