Email Advertising: Telltale Indicators That Your SMTP Server Is Overloaded


In addition to promoting adverts and product offers to your clients, email marketing is also a terrific way to keep in touch with them, which keeps them interested in and returning to your websites. You may notice an increase in your monthly email volume due to these promotions, advertisements, and newsletters. At this point, you’ll encounter difficulties sending mass amounts of email over the Internet, particularly to significant ISPs like Yahoo, Hotmail, and AOL accounts. To learn more, check out NitroMail

You recognize that your current email infrastructure may be unable to keep up with the volume of messages you’re sending. For example, your Hotmail messages sit in queues for long periods, and some are never delivered. If this happens, it might be time to look into more advanced email client options.

An SMTP server is a crucial component of any email marketing infrastructure. Just how vital is this server, anyway? The MTA (mail transfer agent) or SMTP server sends the emails to your bulk email system. This server accepts messages from your email marketing software, filters them based on the domains specified in your delivery list, and then transports and delivers them to the addresses specified. Your email won’t leave your server unless you use an SMTP server.

Envision a stack of unopened mail sitting on your desk since there is no post office to process and deliver the mail. Many organizations used in-house email servers like Exchange or publicly available SMTP servers like Sendmail, Postfix, or Microsoft IIS SMTP servers in the early days of email marketing when volumes were substantially lower.

But two things started to occur when email marketing became more common, and quantities rose. One reason was that in-house email systems designed for individual usage began to crash under the strain of massive amounts of bulk email.

Second, publicly available SMTP servers did not sufficiently address the difficulties in delivering mass emails to the significant consumer ISP domains. Supporting email authentication protocols like DomainKeys, DKIM, SenderID, and SPF and handling email bounces are all examples of these difficulties.

Some warning indications are as follows:

Delayed Shipping

If it takes a long time for even tens of thousands of emails to be sent, it could be because your SMTP server is overburdened with processing the messages and doing the necessary DNS lookups. The second possible cause of your delivery delays is that the recipient’s Internet service provider holds your email until later.

There are many reasons why email is delayed: Your Internet service provider (ISP) may temporarily stop accepting email from your IP address for one of two reasons: 1) your To, From, and IP address are unfamiliar to 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 an email at a rate that is beyond the threshold of the ISP.

Messages addressed to specific domains are being bounced.

The ISP may have placed your IP address on a blocklist if you cannot send emails to specific domains, such as or There are several possible causes for this. First, you may get marked as spam because of the many complaints you receive from recipients. You may be exceeding the ISP’s rate limits for outgoing email transmissions.

If an Internet service provider (ISP) determines that you have suspicious sending habits, it may place your IP address on a blocklist and stop receiving emails from you. A third possibility is that you are flooding the ISP with invalid email addresses. If you have terrible email addresses on your list and keep sending them to them, your ISP may label you as a spammer and block your IP address.

The volume of emails is growing, while responses are either the same or decreasing.

According to the law of averages, if a particular fraction of emails receives a reply, the proportion of emails receiving a reply should grow proportionally as the number of emails sent grows. Therefore, there may be a systemic issue with your email delivery if the percentage of delivered messages declines or remains constant as your inbox volume grows.

This decreased deliverability could be due to any of the issues above. Use of email authentication standards, DNS settings, sending frequency, list quality, and email throttling within the restrictions of your ISP can all affect the overall deliverability of your messages.

When your monthly email volume exceeds a few hundred thousand to a few million, you will see these problems. Unfortunately, low-cost and publicly-available SMTP servers were never designed to handle significant volumes of email or the deliverability challenges associated with sending to the major ISPs. To shield your investment in email marketing, consider a business-grade, commercially accessible SMTP Server or a Hosted SMTP Relay Service provider that meets the needs of high throughput and good deliverability.

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