[Under the Radar]

Why is it frowned upon?

You want assistance from a woman who introduces herself to you as "Mrs. James Doe"? ;^)

If I were to introduce myself to you as “Jane Doe,” you might well assume that I would like to be addressed as “Jane” in our informal society. If I wish to indicate that I would like to be called "Mrs. Doe" instead, the easiest way is by using "Mrs. Jane Doe.”

However, I cannot expect anyone to address me as "Mrs." unless I give them the information from the get-go. So, in my e-mail sig and directories I am (incorrectly) "Mrs. Jane Doe," not (correctly) "Mrs. James Doe."

BTW, this applies to a lot of business settings. It is frustrating to find out that you need to e-mail "Chris Roe" but don't know if Chris is "Mr." or "Ms." Our informality is self-perpetuating.

[Xenalyte]

I'm led to understand that if a woman doesn't indicate preference (as you're doing quite nicely), it's acceptable to refer to her as Ms. Some may take umbrage, but they're usually the ones who didn't tell you Mrs. to begin with, and expect you to just know it. ;)