Does it feel like your inbox is always full? A report from Experian Marketing Services might explain why: It showed clients' email volume rose 5.4 percent in the fourth quarter of 2012 versus a year earlier. The biggest volume increase came from the travel category, which jumped 21 percent, followed by publishers (14 percent) and consumer products/services (10 percent). Flooding consumers' inboxes with email isn't necessarily having the desired effect, though. Experian's analysis showed that click rates were highest on the weekend, when email volume also was the lowest of all the days of the week.