I read an interesting article in eMarketer about the popularity of email among retailers during this past holiday season. Advertising agency Smith-Harmon found that retail email marketers accelerated their email campaigns beginning in October, and on average sent customers more than 14.6 emails in December alone.

"Retailers ratcheted up their email marketing campaigns to aggressively compete for consumers' dwindling spending dollars," said Jeffrey Grau, a senior analyst for eMarketer.

Incidentally, Jeffrey interviewed me in January for a report he has just written on the continued strength of retail email marketing despite the economic downturn. He was kind enough to send me a copy recently. You’ll have to purchase the report to get the in-depth analysis, but in a nutshell, email marketing is thriving in the recession because of its comparative low cost, high ROI and focus on customer retention.

Although these factors illustrate why email is an ideal marketing channel during a recession, the other side of the coin—and one we must be ever mindful of—is that a good thing can be taken too far. If marketers aren’t careful, they risk undermining the value of the inbox.

In fact, in a recent meeting with one of our consumer-packaged-goods clients, one of its executives jokingly asked me if we could tell our retail customers to lower their volumes a bit. "The inbox is getting a little crowded these days," he said.