I got this question recently:
“Is it bad form to send multiple query letters to agents within the same company?”
I posed this question to Script Doctor Eric who has worked for literary agents and this is his reply: “I’d say that if it’s weeks apart, that’s fine. I wouldn’t send more than one letter to the same company less than two weeks apart. Give it a month to be safe. Otherwise it could look desperate and/or spamy.”
I would say that’s good advice. While you can send out the same query letter to lots of different companies at the same time, I wouldn’t send the same query letter to the same agency at the same time. I would query one specific agent at an agency and then if you haven’t heard anything back in a month I would query another, different, specific agent at the same agency and wait to hear from them for a month. In general even the largest agencies aren’t that small, especially the literary departments, so it’s quite likely that someone would notice multiple letters at the same time and think, as Eric points out above, that it’s a bit spamy.