Email marketing activity among the top 100 American online retailers rose in the week ending October 24th, according to new figures.

The Retail Email Blog’s latest Retail Email Index increased by four percent to 227 last week, with each of the top vendors polled sending 2.3 messages each to subscribers on average.

Friday was the busiest day of the week for email marketing, Chad White noted on the Retail Email Blog, while the week’s activity represented the highest level so far in the year to date.

He said: "Usually Friday is the fourth most popular day of the week to send retail emails, but because Halloween is a week away, that boosted Friday’s numbers."

However, retailers inserted more references to the holiday season compared with those to Halloween, according to the index.

The US Interactive Advertising Bureau published figures earlier this month showing that email marketing expenditure rose by two percent to $230 million in the first half of 2008.