The More tag is a marker you can place in your WordPress posts that breaks up the post into two sections. It’s used to manually determine where the ‘read more’ link is placed when presenting a teaser of a post. WordPress doesn’t respect the More tag in RSS feeds by default, so if your rss feed is set to full or summary, it won’t break your posts as specified by the More tag. I have tried plugins that remedy this, but they fell short so I created my own function.
Fortunately, you can alter the content of RSS content through filters. What we want to have happen is to have a post break at the More tag and set the display of a teaser link (such as “continue reading” or “read more”). The two filters that are relevant are the_content_feed and the_excerpt_rss. These filters are applied before the RSS feed is generated and after regular content filters have been applied.
If your RSS feed is set to full and you want to break the posts up at the more tag position, here is an example function you can modify and place in your ‘functions.php’ file.