You should be sending a minimum of two Goodwill Content emails a month and one Sales email a month to your list. Any less than 2 emails a month and your list will decay.
Some business owners feel that if they email their list more than once a month that they will annoy and cause and lose their list to unsubscribes.
If you acquired the subscriber’s email with his/her knowing consent then this fear is unfounded. However, if the individuals on your list never did actually sign up/consent to receive your emails then you SHOULD be concerned at they would unsubscribe. The way to get around this is to group these ‘non-consent’ emails into their own group. And then start creating, newly, a list which is implicitly and only subscribers who have consented.
There is another thing you should consider if you find yourself feeling insecure about emailing your list more than once a month: if you are sending your list good content then there is no need at all for you to feel the slightest bit that you are spamming them. And then the corollary: you only need to feel you are spamming your list if you are actually sending them mediocre or low-value content. Therefore, if you are curating or creating valuable content and emailing it to your list every week there is little fear.
Only have people on your list of knowingly subscribed. If you insist on using a list where the consent was ‘implied’ or ‘assumed’, then you should compartment this list into its own separate database.