Email marketing continues to grow as a great alternative for not only marketing advertisements and product offers to your customers, but also as way to continue a dialog with your customers that keeps them engaged and coming back to your websites. This combination of offers, ads, and newsletters begins to increase your monthly email volume. It is at this point that you begin to experience some of the challenges of sending bulk email out into the Internet, especially to email addresses that belong to the large ISPs like Yahoo, Hotmail and AOL. You begin to realize that the infrastructure you have in place may now be inadequate to handle the level of email you are sending. Your email is getting stuck in queues for hours, or some email stops getting delivered altogether to your Hotmail addresses. If this is happening, you may need to consider an upgrade to a new level of commercially available email software.

One of the main pieces of an email marketing system is the SMTP server. Why is this server so important? Your SMTP server or MTA (mail transfer agent) is the sending engine of your bulk email system. This server receives generated email from your email marketing application, determines what Email1and1 email domains to deliver it to, and provides the transport and delivery of those messages to the various email domains on your list. Without the SMTP server, your email doesn’t make it out of your site. Picture a pile of un-delivered envelopes that just sit on your desk because there is no post office to sort and delivery them to their destination. In the early days of email marketing when volumes were much lower, many people turned to either their internal email servers like Exchange, or they used freely available SMTP servers like Sendmail, Postfix, or Microsoft IIS SMTP server.

But as the use of email for marketing purposes went up and volumes increased, two things began to happen. One was that using in-house email systems built for personal email communications began to break down because they were not built to handle large volumes of bulk email. Second, was that freely available SMTP servers were not able to adequately address the delivery challenges of sending bulk email to the large consumer ISP domains. These challenges include processing email bounces, throttling email to specific domains and the support for email authentication standards like DomainKeys, DKIM, SenderID and SPF.

Here are some trouble signs for look for:

Long Delivery Times

One main reason you may be experiencing long delivery times for even several thousand email messages is that your SMTP server simply cannot keep up with the load of not only parsing your email messages, but also with all of the DNS lookups that need to take place during delivery. A second reason why you may be experiencing long delivery times is that the ISP you are delivering to is deferring your email. Email gets deferred for several reasons: 1) the combination of your To, From, and IP address are not familiar with the ISP so as an anti-spam technique they will temporarily defer receiving email from your IP address; and 2) your SMTP server is sending email at a rate that is beyond the threshold of the ISP so they may again temporarily defer the email coming from your IP address.

Mail to Specific Domains Is Not Delivered

If email to a specific domain like or is not delivered, it may mean that the ISP has put your IP address on a blacklist. This can happen for several reasons. One reason is that your email is generating too many user complaints; people reviewing your email are designating it as spam. Another reason could be that you continually send email at a rate above the thresholds of the ISP. An ISP may choose to put your IP on a blacklist and refuse email from that IP if it detects that you may be a spammer based on your sending patterns. A third reason could be that you are sending too many bad email addresses to the ISP. If your list contains invalid email addresses, and you continually send to those bad email addresses, an ISP may consider you a spammer and put your IP address on a blacklist.

Email Responses Remain Flat or Decrease While Volume Increases

The law of averages would assume that based on a certain percentage of responses per number of total messages, the number of responses would increase at that same percentage as email volume increases. If you are seeing a decrease or a flat percentage as your email volume increases, it may point to an overall deliverability problem that exists within your email system. This decrease in deliverability may be caused by some or all of the problems discussed above. Overall deliverability of your email can depend on many factors including the use of email authentication standards, your DNS configuration, your sending frequency, the quality of your lists, and the throttling of your email within the guidelines of your ISP.

You will experience these issues once your email approaches several hundred thousand to several million a month. Freely available and inexpensive SMTP servers were never architected to support high levels of email, or the deliverability issues surrounding delivery of email to the large ISPs. Consider looking at an enterprise level, commercially available SMTP Server or a Hosted SMTP Relay Service provider that were built for the demands of both high throughput and high deliverability to protect your email marketing investment.

Christopher R John is Business Development Director for SocketLabs, Inc. SocketLabs specializes in high end   and bulk email solutions for the Windows platform and hosted SMTP Relay Services. For more information on the Hurricane Server Platform for Email Marketing and Transactional Email visit 

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