On my Linux VPS, i am using PHPlist for sending newsletters to 40,000 members.

Before the process takes approx 5-6hrs to send the mails... now after installing the LFD firewall i am able to send the mails in 1-2 days. Even now i have to set a cron to run the command to send the newsletter because it stops automatically after 3500 emails send.

Please tell me there is any specific setting in lfd which stopping the server to send the mails to reduce the server load...?

Are you using CSF/LFD on your VPS, if yes, then I think it has to do something with Process Tracking (PT_LIMIT/PT_INTERVAL) see what values you have there.

yes, using CSF/LFD and value for Enable Process Tracking

PT_LIMIT = 30

PT_INTERVAL = 60

Any reply?