Everyone talks about how popups, browser notifications, splash pages, etc. increase newsletter signups. They work. You will definitely get more signups if you annoy people enough.
However, the other side of the argument is never presented.
How many people are so annoyed that they never return to your site again? The world is in a race to the bottom to interrupt as many people as possible. How about just focusing on good content that people want to read? There have never been any popups on Seth Godin’s website.