I have a growing online business and a dedicated server that I use to send out the occasional newsletter. As it grows past a few thousand customers, I wonder how I can send emails faster without being penalized?

I use PHP PEAR's SMTP Mailer module and began sending my newsletters with a "sleep" of 5 seconds. I did so because I was told basically that "if I send emails too fast, my IP will be banned and my host will be pissed".

First run of newsletters sent, no ban, great.

I lowered the "sleep" count to 2 seconds, 1 second, and now half a second using usleep.

But still, I want to post faster.

The reason being is I just realized usleep is killing my CPU levels on my dedicated server and forcing my PHPBB forums into displaying the error "Sorry but the board is temporarily unavailable, please try again in a few minutes" because of a CPU overload of some kind. The WHM load manager is reading over 1.0, not good!

So... how fast is too fast?

Can I send 100 emails per second? 1,000? If not, what or who is stopping me? Is the number of emails per second an old wives tale?


I'd rather not take any risks – if you are on blacklists, getting back out of them will be a pain. There are lots of services like TinyMail/Mailchimp that Just Work™ and offload all the problems.

(If you don't like outsourcing it, I'd at least move it to a different server – no more performance penalties, and if you do happen to be blacklisted, you still have a reserve server in case you do need to send some mails out before the mail server is unlisted).

  • I'd rather not take any risks either, I just find it hard to believe that there are not more concrete details on this sort of thing. I send over 50,000 emails at a time when I issue newsletters, and that is only once every few months. The next time I issue one will probably be 75k subscribers or more. Email services are not economically feasible for a person in my situation unfortunately. – darkAsPitch Feb 26 '12 at 9:29
  • There's probably no concrete details because it a) varies from host to host and b) concrete information would also be useful to malicious users (e.g. stay juuust under the limit of viagra mails/second). – Creshal Feb 26 '12 at 11:06
  • I think these are all terrible answers. Yes, sure, using Mailchimp and Aweber or Postmarkapp or whatever, doesnt help those of us trying to build proper newsletter solutions. If every time this question pops up, the answer is: use so and so, no one is ever going to learn anything. So perhaps instead of proposing alternatives, why not offer actual solutions. #justsaying – coderama Mar 5 '15 at 5:58
  • That's why I elaborated: There's no concrete "do this and you're safe" answer. Every mail hoster has different limits they enforce (which can change based on the sender's reputation or other factors). If you do want to build your own service, you have to test it out yourself, and you need to have contingencies in place because somewhere, someone will put you (if just temporarily) on a blacklist. – Creshal Mar 5 '15 at 10:48

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