Mail not being sent with exim4

Hello,
I have been trying to get the comment_subscribe module working for several days now on my drupal 6.2 site. As far as I know I am enabling it correctly, according to the README.txt file and other module installation documentation. Also I have successfully enabled several other contributed modules, so I THINK I am doing it correctly. Please let me know if there are special steps needed to enable comment_subscribe that I could be missing.

Here is the error message displayed at the top of the page when I add a comment that should send an email:

* warning: pg_query() [function.pg-query]: Query failed: ERROR: syntax error at or near "mail" LINE 3: c.mail) mail FROM z_commentsubscribe zc ^ in /var/www/drupal/includes/database.pgsql.inc on line 138.
* user warning: query: SELECT parents, IF(length(c.mail)<1, ifnull(u.mail,u.init), c.mail) mail FROM z_commentsubscribe zc LEFT JOIN comments c on zc.cid = c.cid LEFT JOIN users u on u.uid = c.uid WHERE zc.cid = 23 in /var/www/drupal/modules/comment_subscribe/comment_subscribe.module on line 259.
* warning: pg_query() [function.pg-query]: Query failed: ERROR: syntax error at or near "mail" LINE 3: c.mail) mail ^ in /var/www/drupal/includes/database.pgsql.inc on line 138.
* user warning: query: SELECT DISTINCT c.cid,u.init,c.uid,c.name,c.nid , IF(length(c.mail)<1, ifnull(u.mail,u.init), c.mail) mail FROM comments c LEFT OUTER JOIN users u ON u.uid=c.uid LEFT JOIN z_commentsubscribe zc on zc.cid=c.cid WHERE nid=2 AND ((zc.cid IN () AND subscribe=1) OR subscribenode=1 )AND c.status=0 AND LENGTH(IF(LENGTH(c.mail)<1, ifnull(u.mail,u.init),c.mail))>1 AND IF(LENGTH(c.mail)<1, ifnull(u.mail,u.init),c.mail) like '%@%.%' AND IF(LENGTH(c.mail)<1, ifnull(u.mail,u.init),c.mail) <> '' GROUP BY IF(LENGTH(c.mail)<1, ifnull(u.mail,u.init),c.mail) ORDER BY mail DESC in /var/www/drupal/modules/comment_subscribe/comment_subscribe.module on line 284.

I am using exim4 as the mail program on this server, could exim4 or it's configuration be the problem? Any help you could give me would be much appreciated.
I have thoroughly searched for a solution but to no avail. If this issue has been dealt with in the past please could you direct me to it's solution. If this is not the correct place for this support request, please let me know where a more appropriate one would be.
Thanks in advance.