The answer to this question will come from your recipients.
Always have in mind that nowadays people are far more busy than before and tons of emails reaches their inboxes. So if you want to keep your recipients happy and read your newsletters learn from them. Checking reports and statistcs is one of the best ways.
You should find a balance between sending a newsletter often and keep the quality of your contect.
If you have lot of things to say it is better to say less and send a newsletter as often as you think, than send it with big content. If a user opens his email and sees a small scrollbar then propably he will leave it in order to read it later and forget it.
If you send a newsletter every day and you see a big number of unsubscribed then propably you should try and send it less frequently, let’s say every 2-3 days.
If you send a newsletter once a month propably your recipients will forget about you. So try to send twice a month and check open rates to see any differences.
What you should think is that the email is the door that someone opens and enters you shop. So what you want is to enter your shop in order to buy stuff and not just stand outside the door. In your shop there are lots of things to see and buy, than just 2-3 posters showing outside.