I just updated my Akismet to 2.2.4 and was facing too many problem related to
"Warning: Cannot modify header information - headers already sent by (output started at /home/chetan/public_html/wp-content/plugins/akismet/akismet.php:936)"
I just downloaded the Akismet.php file and seen one problem in code. It has space at the end of file. Removing that space stops my error. [Line:945]
I hope this info is useful for Akismet developers.