UPDATE: The RSS Feed Submitter has now been removed from IMAutomator
The RSS Feed submission tool works in a very similar way to the Bookmarking tool but the ways in which it can benefit you in terms of SEO is quite different and often misunderstood. I'll use the example of a blog to describe the way these two things work. If you use popular blogging software such as WordPress, Blogger or many others, whenever you publish a new blog post a couple of things will happen - firstly a permanent link will be created to your new blog post, and secondly, the RSS feed of your blog will be uppdated to include that link.
An RSS feed is a resource that shows the latest content from a source and the key thing about RSS is that it is updated automatically! So in the case of a blog, each new post will cause the RSS feed for that blog to be updated with the link to that blog post and this happens behind the scenes. By submitting the RSS feed to directories, you provide another way for your blog content to get syndicated and another way to distribute your backlinks.
Many Posts, Just One Feed
Most websites have just a single RSS feed and if you use software such as WordPress to manage your site, that feed is created for you automatically. There are also tools to allow you create additional feeds yourself but these are not often useful for submission as I shall explain...
IMAutomator submits your RSS feed to directories that are specifically designed for feeds and what they do is to monitor your feeds and index the individual posts inside them. Thus, when you create a new blog post (I am continuing with the blog example here as all blogs have feeds), the entry for your RSS feed in those directories will automatically be updated with your latest content without you having to do anything! Thus, one major difference between bookmark and RSS submission is that you would generally bookmark each individual piece of content but with RSS, you submit your feed just once and you're done! This makes it a great value way to get backlinks as paying for a single RSS submission can get you many backlinks over time!
Finding your RSS Feed
If you are unsure what the URL of your RSS feed is, it is quite easy to find, especially if you are using the Firefox browser. Using Firefox, if you load your website and look in the address bar, if a valid RSS feed is found on that page, an orange RSS icon will be shown on the right of the address bar. Clicking on it will load the feed and you can then highlight the URL. A video accompanying this article will demonstrate this more easily.
Additional RSS Feeds
If you're using software such as WordPress, some additional feeds are created. For example, there will be one for the posts and another for the comments. Should you submit both? Yes! The comments feed contains entries for the comments made on your blog posts and includes the link to your post that had the comment so this is additional backlinks to your posts. In addition, WordPress will also create a separate feed for each category which is particularly useful if you run a large blog with many topics. You can submit each of these feeds as well as the main ones and they will be updated every time you add a post to that category.
There are also additional tools around to create arbitrary RSS feeds from content in all sorts of ways but whether or not they are useful for SEO is debateable. If an RSS feed contains your backlinks then it is worthwhile to submit it - but creating random feeds to static content on your site is of little benefit because if the content within the feed is not updated with new links then no new backlinks are created from it.