No, I am not talking about any black-hat method. It’s completely legitimate, just making use of all the resources at disposal. Let me show you how this trick worked for me and how it can work for you too!

I assume that you use Feedburner as your RSS aggregator

1. Log-in to your Feedburner account.
2. Under Analyze tab , click on Subscribers. Scroll down a bit and you will see “FeedBurner Email Subscriptions”. Expand that link and you will see “Manage you Email Subscriber List”. Click on it.
3. Next page you will see Total Subscribers. Did you notice something? The total subscribers count is different than Feedburner Email subscriptions count given on the previous page. The reason is – Total subscribers count shows you the number of people who opted to subscribe to your RSS by Email while Feedburner  Email subscriptions count shows you the number of people who opted to subscribe to your RSS by Email and have also activated their subscriptions. This is where lies the whole trick. We will now find those people who have opted to subscribe but for some reason have not activated their subscription
4. Click on Export CSV. Save this file to your desktop. Double click to open it. You will find data in 3 columns namely Email, Subscribes and Status. Click on this row.
5. Go to Data > Filter > Auto Filter. You will get data in dropdowns. 
6. Click on Pending Verification under status column. All the email subscribers with status as Pending Verification would be shown. In my case there were about 850+ entries.
7. The task is to send a gentle email to all these subscribers reminding that though they have opted to subscribe but have not yet made the final confirmation.

Did I say 3 days?

Well, I use Gmail as my email service provider. It has a limit of 500 mails to be sent per day otherwise Gmail account might face a temporary ban. To be on the safe side, I sent mails to 300 people per day.

After 3 days, there was a increase in more than 600 subscribers. [Normally, I get only 20 subscribers per day].

Easy, right? Let me know if this worked for you.

Gozar!

How I increased my RSS subscriber count by 600 in 3 days is a post from ReviewOfWeb