It also allows former subscribers to resubscribe when they come across an old issue. Finally, it allows those reading pass along copies to easily subscribe. Exchange ads with other ezine publishers. Make these ads your well tested ads seeking new subscribers. If you offer more than one way to subscribe give them all.
Some people prefer using email to subscribe, others prefer using an online form.
Make it easy for the potential subscriber to use his preference. Purchase ezine ads in carefully chosen publications. Again, make these your well tested ads seeking new subscribers. Keep using the ads that work and stop using those that don't. Swap editorial recommendations with other well written ezines.