Most bloggers focus on their RSS subscribers, but I often remind people that around half of my subscribers subscribe via email using Feedburners email subscription feature.
While this free service is brilliant, it does have a couple of issues you need to be aware of.
First while your overall count is added to when people sign up, unlike if you were using a competing email service like aweber, your count can vary or be lower than you would think, even when people do not unsubscribe. This is because after signing up the new user has to click a confirmation link and they have to continue to receive emails.
Luckily you can download your subscriber list and email those unconfirmed users with a gentle reminder. Obviously one reason they might not have confirmed is they mistyped their email address, happens a lot more often than you would have thought.
Email delivery errors also contributes to the second issue. Feedburner keeps trying to email confirmed but problematic addresses and after five attempts halts service for them. These will be deactivated completely if you do not go in and manually reactivate them in your Feedburner interface (see below).
I recommend taking a look at any problematic email subscribers every few weeks to ensure delivery. Also consider using a plugin to email unconfirmed subscribers.
Have you got any subscriber maintenance tips to share?