Our good friend, Ken Pfeiffer Director of Deliverability for Blue Sky Factory, asked us this year if he could do a guest blog post here and of course we jumped on that great opportunity to have a well respected and trusted person in the industry post for us. Thanks to Ken and the Blue Sky Factory team for sharing this!
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As the Director of Deliverability for Blue Sky Factory, an Email Service Provider (ESP), the question I get asked the most often is, "how fast can you send my mail?"
This is a great question with a very simply answer; one that is the same every time I respond: We can deliver as fast as the receiving mail server will accept. This can be a little difficult for some people to understand.
Most of us are accustomed to near instantaneous delivery. Think about it. If I send a one-off email to you, it's likely that you'll receive it within minutes, if not seconds. There may be a slight delay, but for the most part after you click your send button that email shows up in quick order to the recipient. ESPs on the other hand are senders of bulk email. So rather than just sending email to one recipient at a time, ESP’s send and transmit multiple emails at one time to the receiving mail server. When I say ‘multiple’ I mean hundreds or thousands or even millions!
Nearly all ESPs use Mail Transfer Agents (MTAs). An MTA is software that is used to transmit email from the sender server to the receiving server. ESPs use MTAs to optimize email delivery and a good MTA will allow configuration based on the limits of the receiving mail server. The larger Internet Service Providers (ISPs) have published settings for bulk mailers that will outline how many emails over what period of time they will accept. Many ISP publish these settings on their postmaster FAQ pages for example (http://security.comcast.net/get-help/comcast-post-master-page.aspx and http://postmaster.info.aol.com/faq/mailerfaq.html#msgconn). These are the ISP’s way of saying – if you want to send bulk mail to us, this how you should do it.
Take for example AOL – they state you can’t send email to more than 100 recipients per message and no more than 1,000 recipients per connection. The senders MTA should be configured with these values in order to follow with AOL’s specific limits. If you try and send 2,000 emails to AOL over one connection they will start rejecting your email. Another scenario to mention is rate limiting. Some ISP’s rate limit the number of messages you can send for a given time period. Road Runner limits you to 1,000 messages per hour to non-whitelisted IP’s. So if you have to send 10,000 emails to Road Runner subscribers you better make sure you only send to 1,000 per hour or you will see your email bounce. If an ESP were to ignore these settings then most likely Road Runner would begin to reject connections and the emails would bounce. A bounced email is not what a sender is paying an ESP for. Part of our job is to help clients give their emails every opportunity – for a technology perspective – to be delivered. Whether their emails get blocked or bulked due to content is another story.
Another factor that can influence delivery time is simply just how busy is the receiving ISP. ISP’s receive massive amounts of email daily, they like you have limited amount of computing power at their disposal.
They are only capable of processing so many emails. Think of it this way: ISP’s are a lot like your local highway. It’s usually pretty easy driving, except during rush hour where there are just not enough lanes of traffic to handle all of the cars. So a drive that normally takes 15 minutes might end up taking 45 minutes to an hour. During heavy marketing periods (think Christmas) campaigns that normally in your subscribers’ inbox in 10 minutes might take 30 minutes.
Keep in mind that each ISP will have different limits, so proper MTA configuration is essential. If you have concerns or questions, ask your ESP about their connection settings. From the sender standpoint the best advice I can give is to plan your campaigns carefully with the above factors in mind. If you have a time-sensitive email campaign, be sure to give yourself plenty of lead time to avoid any congestion around sending thresholds and seasonal volume. You may want to consider breaking up your send into a few batches.
I hope I was able to shed a little light on some of the inner workings of email and how it can affect your campaigns and provide a full answer to a question I’m asked all the time.
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Ken Pfeiffer
Director of Deliverability
Don’t just deliver, engage!
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"Nearly all ESPs use Mail Transfer Agents (MTAs). An MTA is software that is used to transmit email from the sender server to the receiving server."
*Nearly* all ESPs? Pray tell, what do the ESPs who don't use MTAs use, carrier pigeons?
An often forgotten limitation is the website behind the links in the mailing. Not many websites can handle handle the burst of clicks from a high volume mailing. It's always a funny to see customers asking for speed, and then discovering that their own website breaks under the load.