Small business put in some hard yards gathering email addresses. Building a subscription base of connections to whom you can send an email to is labour intensive.
Next is writing the email; you need a subject header that gets the reader in and avoids the spam box, and you need to make an offer they can’t refuse.
Once you’ve achieved all that – have you ever wondered exactly how your reader responds..?
Chris Hexton of Vero gets paid to ponder such things. In this linked post he goes into detail without overkill about his investigation into how people respond to the average email, and what you can do to improve yours.
How Your Customers Actually Read Your Emails by Chris Hexton