Getting the right message to the right person is only appropriate if it arrives at the right time. Email marketing constantly poses the million dollar question, "When is the right time to send an email?"
Probably a better question is, "When is the recipient most likely to respond to my email?"
Timing is so intimately tied to what you're sending and to whom, that choosing a certain day, time, or schedule for sending emails is no longer the most efficient tactic. The best thing you can do to ensure relevancy is to focus on list segmentation and targeted emails.
Not everyone on your list is always going to be at an "action point" the moment they receive your email. Therefore, a whole science is dedicated to determining the optimal time to send...
Email marketing frequency and targeted lists go hand in hand. Frequency will not matter unless lists are segmented in a way that applies to the recipient's most recent interaction with your business. You can either segment your lists based on buying cycles - information, purchase, and post-purchase interest emails; or buyer categories - new buyers, active buyers, and inactive buyers.
Once you've segmented your lists, create messages that are standard responses to your recipients' most recent actions. Emails that aren't auto responses ("Thanks for signing up" or "Thank you for your purchase") should include tasteful promotional content that's strategically placed among interesting articles. This ensures that your emails will continue to speak to your subscribers, even when they're not in the mood to buy.
When in doubt, it never hurts to survey your subscribers, asking them how often they prefer to receive your emails.
"Observe due measure, for right timing is, in
all things, the most important factor."
-Hesiod, "Works and Days"