Open rates are down again, according to a study by eROI, an email marketing and research firm. Email continues to be a useful marketing tool, though, despite some drop in open rates.

The study examined email opens by list size and provides numbers that will help affiliates know when and what to send. It found open rates are best on Friday, with Tuesday coming in second.

Still, it’s obvious from the volumes that a lot of people are still reading a lot of email. Email marketing still has a lot of life in it.