Written by
Michael Benson
email-throttling
How many emails does your organization's marketing team dispatch daily? 10? 20? 30? No, probably more. Studies show that the average office worker sends 40 emails per day. Suppose your firm has 20 employees. That translates to 800 email dispatches at the end of each working day.
The crazy part is that it's not just your business doing this. Over 69% of companies globally rely on email marketing, sending approximately 347.3 billion emails daily.
Most successful companies have discovered the tremendous potential of email marketing. And this is where the problem comes in — the emails are just too much. If they were to all land in subscribers' inboxes, recipients would be overwhelmed. That's why several email service providers (ESPs) control the number of emails reaching their clients' mailboxes. Sometimes, doing so requires them to throttle or defer some emails.
So, what does throttle mean? How does email throttling work? What are its potential impacts on email marketing campaigns? And most importantly, how can you prevent it?
In this article, our experts answer these and several other related questions. At the end of your read, you should be able to troubleshoot your email throttling issues and devise practical solutions like a pro.
Throttling can significantly lower your email campaigns' effectiveness. Learn what it entails, understand its causes, and discover how to prevent it. First, let's define throttle from different perspectives.
This term can have two different definitions depending on the affected or implementing party:
Throttling in mailing systems or Email Service Providers (ESPs) is a technique for controlling the email sending rate from a specific IP address (IP throttling) or sender. ESPs use it to prevent bulk email senders from overwhelming their systems. Usually, it results in lower email deliverability, delivery delays, or the deny-listing of suspected spammers.
A common way ESPs implement throttling is by limiting the number of emails their systems can process within a specific duration. Alternatively, they can limit the number of emails a particular sender can send within a specified time. Usually, the better your reputation is, the more emails you can send.
Initially, the ESP may only allow you a few hundred emails per hour. However, as you connect with your customers and build your reputation, the provider will increase your limit. This strategy is known as ramp-up email throttling.
Another technique ESPs can use for throttling emails is to limit the number of emails a particular email address or domain can receive. By doing this, they prevent the overloading of their clients' mailboxes, enhancing user experience.
Email providers or Mailbox Providers (MBPs) can also throttle emails to control the rate at which their servers receive emails. Like ESPs, MBPs use this technique to prevent the overloading of their servers.
MBPs usually throttle emails by limiting the number of connections that a given IP address can establish within a particular period. The exact limit often varies from one MBP to another. It typically depends on an MBP's policy or senders' reputations.
Another strategy MBPs use is recipient throttling. It involves limiting the number of emails a recipient can get from a specific IP address or sender. Like the first technique, it prevents the overwhelming of an MBP's email servers by emails from a particular sender.
The third factor that MBPs can use for throttling is the type of emails. Usually, they prioritize imports and time-sensitive emails. For example, if you want to dispatch time-sensitive information to recipients with whom you have a history, you can add 'Urgent' in the email preheader, subject line, or body. The MBP’s server will instinctively prioritize the email.
However, we recommend using this strategy sparingly. Avoid raising false alarms. Otherwise, your emails might end up in the spam folder. Also, if you have no history with a recipient, do not use time-sensitive descriptions in your email. Doing so might trigger spam filters, damage your reputation, and increase your throttle rates.
While several marketers use email throttling and deferral interchangeably, the two terms mean different things. Throttling is the rejection of an email by the sending server. Unless you retry sending it, it won't reach the recipient. Comparatively, a deferral entails the rejection of an email by the receiving server. Usually, once the sending server has made a delivery attempt but failed, it will automatically retry sending it after some time. So, the latter doesn't require a sender's intervention.
When a sending server has delivered an email to a receiving one, the latter can't throttle it. It can only defer it. However, this is not always the case. Some ESPs do not separate throttling from deferral. That's why, in the previous section, we defined throttling from two perspectives — the sender and the recipient.
As explained above, email throttling can arise because of limitations on the sender or recipient's server. However, when an ESP throttles your emails, it doesn't mean it's not allowing any emails at that particular time. Therefore, the big question is — what makes a service provider throttle your emails as they deliver others? What causes throttling?
Every email service provider seeks to give their clients the best user experience. One way of doing this is ensuring senders don't overwhelm them with too many emails. Therefore, if a provider notices you suddenly increased email traffic to a particular address, they'll likely throttle some. If you want to email your subscribers more often, first establish a rapport with them and then increase your dispatches gradually.
ESPs can also throttle your emails because they sound too alarmist. Unless you have a considerable history with a recipient, overusing phrases like Urgent, Free, Guarantee, You Can't Miss This, and Win Now in your email can position you as an untrustworthy sender. The less reputable email servers perceive you to be, the higher the chances they'll throttle your emails. Even if you have an established relationship with the recipient, use such terms sparingly.
Another factor ESPs can use to decide whether to throttle your emails is how recipients interact with your messages. Have most subscribers marked your emails as spam? Do your emails record poor open, response, and click-through rates?
These patterns automatically show email servers that recipients don't like interacting with your emails. Therefore, if the ESPs servers are almost overwhelmed, your emails will be the perfect option for throttling. The recipients don't want to see them anyway.
Including many images and links can make your email seem spammy and suspicious. It can damage your reputation with an ESP, putting you on their red alarm list. And reasonably so — spammers often use email links to dupe unsuspecting recipients into visiting malicious sites.
If you must use a link or image, limit them to one per email copy. Otherwise, even if you escape throttling, your emails can still trigger spam filters. If you can embed your link into an image, the better.
If you just started using email marketing or switched to a new domain or IP address, the ESP might subject you to ramp-up throttling (gradually increasing your sending limit). Sometimes, the ramping up might take several days or weeks to ensure you learn the ropes of responsible emailing. If you exceed your sending limit within this period, the ESP will likely throttle your excess mail.
Several MBPs and ESPs implement throttling during off-peak hours and weekends. This strategy helps them ensure that the sender's inboxes are not overflowing with irrelevant emails when they resume work. Therefore, sending emails outside regular working hours can also increase your throttling rates, harming your email deliverability.
Every marketer aims to ensure their email messages reach recipients on time. Throttling us adverse to this objective. Below are a few ways this menace can detail your email marketing campaigns:
Email deliverability is a metric marketers use to measure the number of emails reaching subscribers' inboxes (not the spam folder). A lower deliverability rate means most of your emails are bouncing off.
Deliverability Rate = (Delivered Emails ÷ Total Emails Sent) × 100
Suppose you sent 10,000 emails. If the sending server delivered 8,000 emails and the receiving server throttled 1,000, your deliverability rate would be 70%, {(7,000÷10,000) × 100}.
As elaborated above, throttling can significantly enhance your deliverability rate. The lower this rate, the less the number of subscribers receiving your email messages. If unchecked, this can substantially lower your campaign's ROI.
Besides harming your email deliverability, throttling can also lower your delivery rates. Unlike the deliverability rate, the delivery rate accounts for all the delivered emails (including those landing in the junk folder). For instance, in the example above, the delivery rate is 80%, {(8,000÷10,000) × 100}.
If the throttling comes from the sending server's side, it lowers the delivery rate. If it comes from the receiving server's side, it can affect the delivery and deliverability rates simultaneously.
Email marketing campaigns always have timelines. Sometimes, marketers customize messages with date stamps and date-specific offers. If throttling occurs, these emails will be delivered later than expected, making their messages stale.
For example, imagine if your company had a specific discount for Labor Day. The best time to inform your customers of this offer is September 4th or a day earlier. However, if you were to encounter a throttling issue, your subscribers will get the update a few days after Labor Day.
Will the offer still be relevant? No. Even if it gets you a few sales, the success rate will be lower than it would have been if the email had arrived on time.
Before beginning an email marketing campaign, businesses often set target ROIs with clear key performance indicators. Doing so enables them to monitor the success of these initiatives and identify areas that require adjustments. In an ideal world, a well-planned campaign should generate a consistent ROI. However, with delayed or failed deliveries because of throttling, it's often challenging to monitor email performance.
Now that you understand how throttling works, let's discuss how you can identify if an ESP is throttling your emails. Are you receiving any of the following error messages?
If you've been getting these standard throttling error messages more frequently, you should rethink your email marketing strategies. The chances are you're making some of the mistakes we outlined in the previous section.
Another way to identify if an ESP is throttling your emails is to monitor your deliverability signals. While low deliverability can result from varying factors, such as poor list quality and overuse of spam trigger words, an increase in the frequency of temporary failures and soft bounces often signifies throttling issues.
There's no standard procedure for handling throttling issues. Different ESPs require varying interventions. That said, below are a few recommendations for managing this problem.
Fortunately, email throttling is remediable and preventable. Below are a few best practices to reduce your throttling rates:
Different ESPs have varying limits on the number of emails a specific domain or IP address can process within a particular time. Monitor your throttling patterns to learn your limits. Some ESPs allow businesses to request an expansion of their limits.
Emailing can sometimes be a tedious and time-consuming job. We understand the temptation to send all your emails once and get done with it. However, this approach will land you in trouble. If you don't have the time to send emails daily, you can use a scheduler or automation tool to spread them throughout the day or week. Doing so ensures you stay within your assigned limits.
When using a conventional email marketing platform, you share the IP address with several other senders. As a result, you won't have full control over your IP address's reputation. Sometimes, mistakes by other senders can put you on the denylist, making you susceptible to throttling. Comparatively, when using a dedicated IP address, you have total control over your reputation.
Your reputation is inarguably the most crucial determinant of whether an ESP will throttle your emails or deliver them. A poor reputation automatically puts you in the bad books.
Each email matters. Before clicking the Send button, ensure the email doesn't sound spammy. Avoid screaming subject lines and preheaders, personalize the email message for each recipient, and keep the email body precise and direct.
The trick is to be recipient-centric. Put yourself in your subscribers' shoes. If any of the details in your email wouldn't add value to you as a recipient, omit it. Doing so can reduce the number of times subscribers mark your emails as spam, increase your open and click-through, and improve your reputation.
If you have a new domain or IP address, do not go into bulk dispatches right away. Instead, start small, establish rapport with your recipients, and warm the address up before going large-scale. Warming up ensures you don’t come out as a spammer and thus reducing your likelihood of being blacklisted. This practice can also help you create a good sender reputation for your IP address.
Differentiate your domain from other malicious addresses that might impersonate you. Register it on authentication protocols like DMARC, SPF, and DKIM. Several ESPs consider authenticated email addresses reputable, reducing your chances of getting throttling alerts.
Authenticating your domains also boosts your reputation to the recipient receiving the email as they’re sure that they’re not dealing with impostors.
Above everything else, take your recipients' user experience (UX) seriously. Don’t just throw them any email you feel like writing, as this may damage your sender’s reputation and have your address blacklisted. Throttling is a defense mechanism by ESPs to safeguard their clients from spammers that might harm their UX. Therefore, if you deliberately try to improve your subscribers' UX, you will gain favor with ESP algorithms, reducing your chances of email throttling. And the opposite is true.
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