There's no one right answer to the question: how often should I send email?
Your list will include a segment of people who think you're sending too much, and another segment of people who'd happily receive emails from you more often.
There's probably not even a single frequency that's right for your whole list
Different kinds of recipient may want different frequencies. Someone who buys from you once or twice a year may be happy with a monthly message; someone who buys more often may well prefer more frequent messages. You need to look at your list and target different segments with the frequency that's suitable for them.
Some people on your list actually want more emails from you
A customer who makes purchases from you every 2-3 months would most likely appreciate a weekly email. If you're just sending them a monthly newsletter, you're probably actually doing them a disservice.
People will gladly accept your emails if they know it's keeping costs down
Some marketers seem to think there's something inherently distasteful about sending out emails at all. But if using email allows you to reduce the cost of sending offers to people, they'll prefer a "grubby" email with low prices to a glossy TV ad that pushes prices up - especially in today's economic climate.
