Creating an email list that works involves a lot of time, effort, scrutiny, and patience. You invest that much in it because it provides the single best return on investment in all your marketing channels. Of course, if your recipients don’t read your email message, much less open them, that ROI can be impossible to achieve.
Build trust with your IP by sending small batches of emails.
ISP filters are designed to reject spam emails. You need to ‘convince’ these filters that your emails are not spam, so the first thing you should do is send out emails in small batches, and send them only to your most loyal customers. Once your IP detects that your emails are being received and opened by users, it will start to trust you. You may then increase the number of emails gradually.
Make sure that marketing emails aren’t sent to non-existent users.
Sending your marketing emails to deleted or wrong accounts can increase your bounce rate and damage your credibility as an email marketer. Review your list every now and then and filter out all users who have not clicked or opened your emails after a few months.
Send your emails at the right frequency.
Sending out too much can fatigue your audience and destroy your revenue. Thus, you need to send just the right number of emails. Finding the perfect number requires intricate study, but it can be thoroughly worth it. If you don’t want to go through all that trouble, a good rule of thumb would be to send one email per week.
The year of email deliverability, campaignmonitor.com
12 Ways to Improve Email Deliverability, blog.kissmetrics.com