This refers to how often one of your customers should get an email from you. This, of course, depends on your business and strategy.
What we suggest is using major interactions such as cart abandonment, order completion, receipt, shipping notification, etc. as triggers. This will help you stay relevant and timely.
Keep in mind that providers such as Mandrill (Mail Chimp) have hourly quotas for the number of emails that can go through. Quotas are automatically calculated on your reputation. The lower it is, the fewer emails per hour you can send.
So if you try to email everybody on your list at once, this will most probably exceed your quota and emails will get stuck in a sending queue and then get deleted (in Mandrill it happens after 48 hours).
That’s why it’s better to segment customers into smaller groups and send them separate campaigns. The added benefit is more relevant offers and they won’t feel spammed too often.
In Metrilo’s Targeted Email Campaigns feature, there’s this awesome option to leave out people whom you have sent an email in the last [select number] days. So you never spam again!