Marketers need to be guardians of permission -- and that includes keeping subscribers' email addresses out of the hands of partners and even sister brands.

Thankfully this is not a widespread problem in the retail space, but I recently started receiving emails from a retailer's sister brand and another retailer's partner. In both cases, my permission was not sought.

Last month, after more than a year of being a Drugstore.com email subscriber, I started receiving emails from VisionDirect, a partner whose site is "powered by Drugstore.com." The initial email from them indicated that I was a prior customer that they wanted to reengage. However, I was never a customer or subscriber to its email program.

What this tells me is that Drugstore.com violated my privacy expectations by sharing my address with VisionDirect, which then used it in a way that makes it look foolish and Drugstore.com irresponsible. It may have even violated its privacy policy, although it's difficult to tell considering all the vague language.

Recently I also started receiving emails from The Popcorn Factory, which is a division of 1-800-Flowers. While I am a subscriber to 1-800-Flowers' email program, I never opted in to receive communications from The Popcorn Factory, nor was I informed during the subscription process that I could opt-in to receive emails from this sister brand.

Even worse, 1-800-Flowers never made an attempt to introduce me to its popcorn brand, and the Popcorn Factory's emails don't identify the company as owned by 1-800-Flowers. So there's no connection between The Popcorn Factory and the brand I'm familiar with, 1-800-Flowers. That's a surefire way to generate spam complaints in a hurry.

Here are some ways to introduce your subscribers to your sister brands and partners:

1.     During the sign-up process, present customers with the opportunity to subscribe to sister brands. Of all the retailers included in my 2007 Retail Email Subscription Benchmark Study, only the Gap Inc. brands did this. So, for instance, when you subscribe to Banana Republic's newsletter, you're prompted to subscribe to the newsletters offered by Old Navy, Gap and Piperlime as well.

2.     Send an email of introduction from your domain and give your subscribers an opportunity to sign up for the sister brand or partners' email program.

3.     Highlight the sister brand or partner in your regular emails, preferably in a way that relates it to your offerings. For instance, in a March 6 email from Banana Republic, there was a secondary banner about some shoes from Piperlime, the shoe store brand that Gap Inc. launched late last year, that coordinated with the pants that Banana Republic was promoting in that email. That's a highly relevant way of incorporating a reference.

4.     Include links to sister brands and partners as part of your email template, but only if the brands are complementary. Also avoid this tactic if there's a risk of blurring the lines between two brands. RitzCamera is one retailer that includes links to its sister brands, which include BoatersWorld.com and FishingOnly.com. While I question the synergies between RitzCamera and BoatersWorld, there are presumably much stronger synergies between BoatersWorld and FishingOnly so those two brands' emails could have links to each other.

One of the methods that I don't recommend is repeatedly sending email on behalf of the other brand using your domain. When Gap Inc. was introducing their Piperlime shoe store brand, for months and months on end they sent what were essentially Piperlime emails to the subscribers of the Gap, Old Navy and Banana Republic newsletters. While on a few occasions, the emails would try to recruit subscribers for Piperlime's email program, usually they would just promote Piperlime's products. That tactic hurts the relevancy of your email program because you're no longer sending the content your subscribers signed up for and expect.

Don't abuse your subscribers' permission, because once you lose it it's nearly impossible to get back.