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A lot of ISP rate limit the amount of e-mails that is sent from a particular IP address. What is the proper way to get around that rate limit?

Our company has an iPhone application that sends many e-mails because of our large user base and many e-mails go to different ISPs that rate limit the number of messages coming from a specific IP.

We do not send spam and we are a legitimate business. However, is there a better way to resolve this limitation rather than just getting a ton of IP addresses?

Ideally, I wouldn't want to rely on a third party service to send mail. However, if its the only possible solution, we would consider.

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What did your ISP say? You did contact them, to discuss the situtation right? – LukeR Feb 19 '10 at 3:53
Just rent a VPS for $20/mo. and be done with it. – jamieb Feb 19 '10 at 3:53
Sorry, who blocks you, your ISP or the receiving servers? try using a pause between each mail you send, like 5 seconds or something. – user144742 Nov 9 '12 at 4:52

If an ISP limits the number of emails from a given source I fail to understand how changing that source would help. Perhaps you need to either:

  1. Find a way to send the emails from multiple sources
  2. Find a better solution altogether

On point 2, if your application is sending so many emails that you are running into such limits how could the recipients even have enough time to read them all? That sounds to me like an absurd amount of email.

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Do you have a web site that may provide SMTP services? Perhaps you can route your emails out through that ISP. While some ISPs block port 25, they typically leave port 26, often used as a work around, or port 587 (smtp submission port) open.

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Just to clarify, you have a bunch of iphones connected by wi-fi at your office sending out email? – jeffatrackaid Feb 19 '10 at 4:11
Good point. Sending out on a non-standard port might work – Mark Henderson Feb 19 '10 at 7:52

Is this a business-class internet connection? Does your contract with the ISP allow you to run servers off of this connection? If so, you should (hopefully) be able to negotiate with your ISP for them to loosen their SMTP rate limiting for you.

Another solution would be to lease a small VPS and relay all your outbound mail through that server (via an ssh tunnel or some other encrypted connection). That would take your ISP out of the loop - they'd have no way of knowing how much mail you were sending out.

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If you can have more than one IP on your server (ie. if your service provider allows you this), you could theoretically add more IPs to your server and set up multiple mail interfaces to split the load, something like this:

         |                           |
         |     SERVER                |
iPhone \          / mailserver1 [IP1] ---> 
...     \        /
iPhone --mail gw--- mailserver2 [IP2] --->
...     / IP1    \
iPhone /          \ mailserver3 [IP3] --->
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We had a similar problem with a large amount of students that forward their email to common ISPs. So when we would send a message to all 20,000 students, thousands of them were forwarding to roadrunner accounts and we were hitting rate limits.

To get around this issue, we found they subscribe to So you pay a nomininal fee and get whitelisted to anyone who subscribes. This worked in our case.

While this worked in our case, all in all I feel this is a crap solution, and feel a little dirty paying for it. You are basically paying a ransom to have your email delivered. And if you are going to multiple ISPs there may be different services.

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I dont think there is a solution, if your ISP has only assigned you 1 ip address.

With all of the iPhones connected via wifi, all the traffic is forced out via the assigned IP address.

There is no way of getting out to the outside execept thhrough the IP that was assigned to you by your ISP.

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The e-mails are coming from our servers not the iPhone itself. – Derek Ting Feb 19 '10 at 4:08
yes, i was aware of that – freddy6 Feb 21 '10 at 13:01

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