Those of us in the technology world (call us nerds, geeks or software developers) assume a 1:1 ratio between personal e-mail addresses and people.

I’m not talking about business addresses (like mine: alan@bzmedia.com) or group addresses (like our customer service address: service@bzmedia.com). I mean your home, non-business address, which might come from your cable TV company, DSL or wireless provider, or from a free e-mail service like Google’s Gmail, Microsoft’s Hotmail, Yahoo, India’s Rediffmail, and so on.

Some people (like myself) have dozens of personal e-mail addresses, some current, some legacy, some active, some dormant, some for friends and family, some for buying things online, some for subscribing to newsgroups, some totally forgotten. So, yes, it’s not really a 1:1 ratio; it’s 1:many, but here “many” means many addresses, not many people.

For techies, you can safely assume that a personal e-mail address is like a personal cellular phone number: It’s personal. All my personal e-mail addresses are for me. My wife has her own personal e-mail addresses. There are no shared addresses in our family.

I would venture that most of you receiving SD Times News on Monday treat your personal e-mail addresses in that way.

Yet I’m continually astonished at how many couples share one personal e-mail address, just like they share one home phone number. Jack and Jill Smith might use the shared address smithfamily@provider.com or smiths@provider.com or jandjsmith@provider.com, and that’s the sole non-business address they have.

This seems to be a generational divide. My parents share one e-mail address. I see a lot of shared personal e-mail addresses in the directories of several non-profit organizations, and even in my teenage son’s school parents directory. The divide seems to be somewhere north of 50 years old:

• Over 70 years old, the spouses most likely share one address. It’s probably from AOL or an Internet service provider.

• Under 50 years old, it’s almost certainly not a shared address, and it’s probably not from AOL or an ISP. But I know many exceptions.

• Between 50 and 70 years old, it could go either way, but it’s more likely to be personal than shared, and probably comes from an ISP.

Why is this relevant? Many of us assume that a non-business address is a personal e-mail address, and therefore is suitable for receiving confidential information. That can be a false assumption—even with couples under 50 years old.

Also, what happens if both spouses try to create accounts on a website that uses an e-mail address as the registration key? Registration systems increasingly rely upon the e-mail address as the unique identifier associated with one, and only one, person.

What’s your experience? Share your thoughts at feedback@bzmedia.com (and yes, that’s a shared account).

Alan Zeichick is editorial director of SD Times. Follow him on Twitter at twitter.com/zeichick. Read his blog at ztrek.blogspot.com.