Emailing tips for ensuring delivery of legitimate high-volume campaigns

Marketers and other business managers look to their IT department for help and some level of assurance that their high-volume email campaigns are reaching their desired mailing list targets. Email delivery experts at SMTP Inc. share their best practices for high-volume email delivery -- ones that also abide by CAN-SPAM rules. Any group that sends email to large distribution lists can benefit from these tips.

It's that time of year again when companies, especially on the B2C side, promote their holiday incentives. In fact, the volume of email in the fourth quarter doubles as vendors send out gift coupons, online catalogs and special holiday promotions.

Even during the other 10 months of the year, companies still have a need to communicate with thousands of their constituents. Monthly e-newsletters must get out. Partners and distributors need to be informed of new products and services. There are countless reasons to send out large batches of email messages. And even in the age of social media and RSS feeds, email is still a critical tool for mass communications.

5 best practices to improve your email delivery success rate

Marketers and other business managers look to their IT department for help and some level of assurance that their high-volume email campaigns are reaching their desired mailing list targets. But the problem is that IT often cannot guarantee a high email delivery success rate. We went to email delivery experts SMTP Inc. of Boston to get a few of their best practices for high-volume email delivery -- ones that also abide by CAN-SPAM rules. Any group that sends email to large distribution lists can benefit from these tips.

Start with a sound and healthy IP address

The IP address you will be using for sending should have a good reputation, and it should not be on any ISP blacklists. It should lay claim to a legitimate history of CAN-SPAM compliant sending. It must not have a record of high recipient complaint rates, generated when they press a "This is Spam" button from their email inbox.

There are different ways to keep track of your IP's reputation online. Return Path's Sender Score, for example, is a leading provider of sender reputation reports and free tools. Check out this free service at

Anything that adds credibility to the IP address, such as previously using the same IP address to successfully send 100,000 emails, helps. However, if all of a sudden you send 1 million emails, the same IP address may fail you because its reputation has not been previously established for the higher volume of 1 million.

IP warm-up

"IP warm-up" is a buzz phrase in the email delivery world that says you should have a procedure to ramp up or "warm up" the IPs to a higher level of sending capability -- for example, sending 100,000 to 1 million emails successfully.

This is a difficult task because it is so time-consuming and a positive result depends on a number of factors. The warm-up process is not quick and usually takes anywhere from two to four weeks. There is no carte blanche and unless you have an inventory of previously warmed IP addresses, you must go through a tedious process of sending a gradually increasing volume of emails to each ISP so they can slowly evaluate your legitimacy as a sender.

For example, if your emails to AOL result in a return message of "temp-failed" (deferred) with the error code "421 RLY:NW," most likely you're sending through an IP address that hasn't been properly warmed. Known as a "block," you usually must wait between 24 and 48 hours before you can resume sending in order to allow AOL to analyze previous history on your IP, and if OK, unblock it.

According to Ruslan Bondarev, CTO of SMTP Inc.,"IP warm-up depends on the ISPs you're sending to, your delivery batch size, the content of your email, and the quality of your mailing list. We usually have pre-warmed IPs to send to the Big Four, namely, Yahoo, Hotmail, Gmail and AOL. Careful analysis of our inventory of warm IPs, matched with specific customer needs, helps us to find the optimum solution for increasing the probability of inbox delivery."

Software load balancing

Once you have a set of warm IPs with good reputation, what do you do next? Well, you need to balance all the traffic you send through these IPs as some of your IPs may be warmed up to send 100,000 emails per day, others may be warmed to send at other volumes, such as 1 million emails per day.

On top of that, because warm-up is always ISP-centric, if you want to pull a huge Hotmail-only delivery, you might want to know how warm each of your IPs are regarding Hotmail, and once you figure that out, you must distribute the delivery across those IPs accordingly. And even after you've done that, you still need to keep an eye out, because an ISP may suddenly, for some reason, refuse to accept or throttle the mailing from one of your IPs, and you will need to accommodate for that by altering your sending distribution in near real time.

This is not a simple task, and there are limited choices available for load balancers equipped with native intelligence that can understand the concept of ISP-centric warm IPs.


After you have finally figured out which IPs to use and when to use them, you can't just sit back and relax while your email is being sent. There's additional heavy lifting involved in analyzing the outcome of your email delivery: spam complaints, bounce ratios, spam filter results (inbox vs. spam folder). All these (and more) will influence your ability to send further emails to any designated ISP and through to the end recipients on your email list. Even when you have a completely warm IP and your distribution volume is by the book, your emails may still get caught up in ISP spam filters. If your list is old and generates a lot of bounced emails, you will soon find yourself in trouble. A high email bounce ratio is a strong indicator for a "dictionary attack" or purchased list, neither of which are tolerated by ISPs.

You must continually clean your list, honor your "unsubscribes," watch changes to your IP reputation, observe ISPs feedback in real-time, and respond accordingly.

"By monitoring the actual feedback from ISPs, we pro-actively help our customers to optimize their delivery by reviewing content for suspect keywords or URLs, pointing out email that is too graphic-rich or contains no text at all, all of which can trigger the email campaign being designated as spam," says SMTP's Bondarev. "Our goal is to help senders communicate with each of their recipients effectively and within compliant best practices."

If following the tips above seems like a lot of work, it is. But consider this. Your marketers and business managers are counting on reaching the people on their distribution lists to drive sales or communicate important information -- none of which will happen if the messages are never delivered. Ruslan Bondarev cites instances where companies had close to 0% delivery due to constant temp failures or blocks and they were able to raise that to about 98% delivery, all because of IP warm-up and no other changes. It shows that a little upfront planning and effort can yield better results in the end.

Linda Musthaler is a principal analyst with Essential Solutions Corporation. You can write to her at


About Essential Solutions Corp:

Essential Solutions researches the practical value of information technology, and how it can make individual workers and entire organizations more productive. Essential Solutions offers consulting services to computer industry and corporate clients to help define and fulfill the potential of IT.

Learn more about this topic

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