Perl Sendmail slowing down on dedicated server.

I have made my own emailer program, but i stump on a problem.

I suppose this problem is server issue and not actually program related, since i first tried my program on another server and there it worked fine even after sending 10 000 emails. (unfortunately i found out that wasnt allowed on that server)

So i went on to rent dedicated server from anotherer place.

However, when i there used my emailer program there were 2 problems.

1. It kept slowing down after each sent email. After about 500 sent emails it was already down to speed of maybe 1 email per second only, and it kept slowing even more.

I found out that if i clicked, i think it was something like "reset internet relay" button or something (cant really remember), then it became speedy again for that little while.

2. after about 5 minutes, it stopped the program even all the emails werent sent. (so basically i was at maximum able to send about 500 emails at once, then needed to click that button again and start sending again)

So question is if someone knows how to fix this problem.

And to point out more - i dont understand much about servers, and hence it might even be just some simple setting somewhere that needs to be changed, but i just wont know how or where.

Anyway, to me it seemed like it was server issue.

I am soon in need of getting dedicated server again, but i would like to know how to fix this probelm first, since at least on that last place they werent willing to give me advice on how to fix that problem or even analyzing problem, since they said their customer service doesnt extend to program problems.