After some fighting with myself I have decided to throw away the FeedBurner-Redirector Plugin.
Many people might say, that was a stupid action – but the reason is simple: Why should WordPress handle things, if the apache webserver can do it better (using less memory)?
This is the syntax of my .htaccess. If someone out there knows a better way, I am thankful for every tip.
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /##### feedburner
### redirect for feedburner feed
RewriteCond %{HTTP_USER_AGENT} ^FeedBurner.*$
RewriteRule ^feed/(feed|rdf|rss|rss2|atom)/?$ /index.php?&feed=$1 [QSA,L]
RewriteCond %{HTTP_USER_AGENT} ^FeedBurner.*$
RewriteRule ^(feed|rdf|rss|rss2|atom)/?$ /index.php?&feed=$1 [QSA,L]# redirect for users not subscribed
RewriteCond %{HTTP_USER_AGENT} !^FeedBurner.*$
RewriteRule ^(feed|rdf|rss|rss2|atom)/?$ http://feeds.feedburner.com/StarBlog [R,L]
RewriteCond %{HTTP_USER_AGENT} !FeedBurner.*$
RewriteRule ^feed/(feed|rdf|rss|rss2|atom)/?$ http://feeds.feedburner.com/StarBlog [R,L]
##### /feedburner# BEGIN WordPress
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]
# END WordPress
</IfModule mod_rewrite.c>