13 Warning Signs of Email Deliverability Problems Ahead

May 15, 2023 | 10 minute read
Daniel Deneweth
Head of Email Deliverability Services, Oracle Digital Experience Agency
Text Size 100%:

Nothing can destroy your email marketing performance quite like email deliverability problems. Whether it’s the slow slip of inbox placement due to diminishing engagement or the sudden collapse due to a blocklisting, it’s always devastating and usually a shock.

But honestly, email deliverability problems are rarely a surprise if you know what to look out for. During my nearly two decades focused on email deliverability, I’ve noticed a number of events that often precede problems:

1. Changing Email Service Providers

This is perhaps the biggest change you can make to your email program. Changing providers is essentially starting from scratch—you have new IP addresses and a new sending subdomain, neither of which have a reputation associated with them. You also need to worry about things like importing the suppression list from your old provider, so that you don’t start off on the wrong foot by mailing a bunch of bad addresses.

It’s wise to work with a deliverability consultant to develop a migration plan optimized for your business, and to have them monitor your inbox placement closely during the ramp up phase, which generally takes 4-6 weeks. Speaking of the warming up process...

3 approaches to simplifying your martech stack.

2. Warming Up a New IP Address

If you change the IP address you send emails from or add a new one, you can’t just start sending tons of emails from the new IP address on day 1. That’s what spammers do, as they jump around from one IP address to another to try to avoid detection. This behavior will get your emails blocked.

Instead, you need to gradually ramp up email volume from a new IP address in a methodical way to give mailbox providers a chance to see that their users are responding positively to it. There’s an ever-changing formula for warming up an IP address properly, and it takes a watchful eye to know when to dial volume back and give the process more time.

3. Warming Up a New Sending Subdomain

Your sending subdomain (i.e., email.brand.com) is just as important as your IP address. Mailbox providers watch both of these closely, which is why you can’t simply change your IP address to run away from a poor sender reputation. Even if you change your sending subdomain, that poor reputation can be tied back to your main domain, which no legitimate business can abandon.

Brands should be even more careful when warming up a new sending subdomain, because the sender reputation associated with it is even stickier than the one associated with your IP address.

4. When Doing High-Volume Ad-Hoc Sends

Privacy policy update, anyone? Once-a-year or one-time emails like this that are sent to your full list—often even disengaged and chronically inactive subscribers—can sometimes lead to deliverability issues. Problems are even more likely when these kinds of emails are also required to be sent to those who have unsubscribed or complained.

Brands should plan for such a large send by considering the regular daily volume for their domain and IPs, and the incremental increase beyond that average send volume. If that volume jump will more than double your daily send volume, it can cause a red flag for mailbox providers who will, in turn, block your mail. It’s also important to watch deliverability closely after sending an email like this, in order to quickly address any delivery issues that crop up as a result. 

5. During Peak Season Sending

With so much business riding on your performance during your peak seasons, it’s the worst time to have email deliverability problems. But your peak seasons are also the peak seasons for your competitors and peers, which often means a spike in emails at mailbox providers, putting them on their guard.

If you’ve experienced deliverability issues in the past during your highest volume seasons, then your risk of problems in the future is even higher. It’s important for senders to prepare in advance for an increase in volume during peak season. We help our clients employ strategies like ramping up in advance and running a reactivation program to bring more people back into their active file long before the pressure is on to send additional campaigns. 

Get quarter-by-quarter advice on how to prepare for a successful holiday season.

6. When Bounce Rates Start to Exceed 3%-5%

There are two types of bounces to be concerned about: 

  1. Hard bounces, which are invalid addresses, either because the address has never been active or because the address was abandoned and then retired by the mailbox provider
  2. Soft bounces, which are temporary blocks by mailbox providers that can be related to things like reputation or volume

The most common reason that emails hard bounce is that the email address you’re trying to send email to doesn’t exist. Spammers often have high bounce rates, because their lists generally have lots of expired and guessed email addresses, since they try to reach the largest audience possible. So, when you send to a lot of bad addresses and your hard bounce rate is high, mailbox providers take this as a sign that you might be a spammer—or at least that you’re being reckless with your subscriber acquisition processes. If your hard bounce rates ever rise above 5% in any given month, it’s a good idea to seek professional help to find the source of the problem that’s causing so many invalid email addresses to get onto your list.

For any large sender, some amount of soft bouncing is normal due to deferrals from smaller mailbox providers that can only accept so much mail at a certain time. However, if you see a soft bounce rate upwards of 3%, especially at the top providers like Gmail and Outlook.com, then you may be getting blocked due to reputation issues. A deliverability consultant can help you identify the root cause, make a plan for improvement, and get the block removed on your behalf, in some cases. 

To get the latest digital marketing and communications advice from the trusted experts at Oracle Digital Experience Agency, subscribe to our award-winning twice-monthly newsletter.

7. When Opening Up a New Subscriber Acquisition Source

Each of your subscriber acquisition sources has a different value-risk mix because they attract subscribers who have different goals, different levels of familiarity with your brand, different expectations, and so on.

For instance, people who opt in during checkout are familiar with your brand and have made at least one purchase. The chances of their email address bouncing is lower, because they want their email receipt, and the likelihood of them being disappointed with your email content is low because they’ve already shown an affinity for your brand by making a purchase and raising their hand to receive your emails.

At the other end of the spectrum are people who are getting onto your email list through, for instance, a sweepstakes or co-registration. People who opt in via a sweepstakes may only be interested in winning a prize and not interested in receiving your emails. And people who opt in via a co-registration form may not be familiar with your brand or may be confusing it with another brand. In either case, these subscribers are at high risk of complaining and unsubscribing.

Because of the different value-risk mix of every subscriber acquisition source, you should watch your deliverability closely when adding a new one.

Get our checklist of 18 different types of audience acquisition source ideas, which includes advice on how to manage their risks.

8. During Periods of Faster-than-Usual List Growth

Track your list size and understand what your baseline list growth is so you can identify any unexpected jumps in list size. This is important because a spike may be a sign of bot signups that could harm your sender reputation and deliverability.

To make aberrant behavior easier to spot, consider tracking individual subscriber acquisition sources. For instance, track the new subscribers you get from your checkout opt-in separately from those you get from the signup form on your homepage. This will help you see potential problems sooner and investigate them more easily.

9. When Email Complaint Rates Start to Exceed 0.2%

Most brands are able to keep their complaint rates well below 0.2%, so exceeding this level is a serious sign of trouble. It’s important to remember that overall complaint rates can be misleading, since Gmail and many smaller mailbox providers do not offer a feedback loop that redirects complaints back to you, skewing this metric to the low side. Complaints should be monitored by recipient domain and by campaign. This metric can also be leveraged to monitor the performance for new signup sources.

Spam complaints are just one of 7 factors that affect email deliverability.

10. When Your Open Rates Drop Dramatically at a Particular Mailbox Provider

Just like tracking new subscribers by acquisition source allows you to see trends more clearly, the same is true of tracking email performance by mailbox provider. This can let you see issues that you might have with a particular provider like Gmail, for example. 

If your engagement metrics seriously dip at one mailbox provider, then that’s likely a sign of being blocked there or having been added to a blocklist that the provider uses to inform their blocking decisions. Very low open rates (in the 1-2% range) can also be a sign of spam folder placement. Deliverability experts know how to read engagement rates to determine if you are trending in the wrong direction or already in trouble. 

11. When Your Open Rates Average 5% or Less at a Particular Mailbox Provider

In addition to big dips in engagement, you want to be on alert for your open rates becoming too low. That’s because mailbox providers use user engagement as a major factor in their filter algorithms. If very few of their users are engaging with your emails, that is a signal to the mailbox provider that you are not targeting intelligently and are mailing to a lot of inactive subscribers. This can result in your mail being flagged as undesirable and sent to spam. 

Changes in the way Apple’s Mail Privacy Protection partially obscures real open signals has reduced some of the historical value of open rates. However, open rates remain an important measure of subscriber engagement. You should be establishing your open rate baseline at a ‘new normal’, and monitoring for negative trends and dips.

Get our Definitive Guide to Adapting to Mail Privacy Protection via this free, no-form download.

12. When You’re Listed by a Small Blocklist

When you’re listed by a major blocklist operator, you could see half or more of all your emails blocked overnight. That’s not a warning sign—it’s a disaster. However, most of these listings aren’t out of the blue. Often, they’re preceded by listings by smaller blocklist operators.

It can be tempting to ignore these listings, since they don’t tend to have much of an impact on a sender’s inbox placement. However, you get the attention of smaller blocklist operators the same way that you get the attention of larger ones: getting too many spam complaints and hitting spam traps. If left unaddressed, these behaviors will soon get you on the radars of more powerful blocklists. So, pay attention to blocklistings by smaller operators and take action to resolve them.

How to get off a blocklist and stay off.

13. When You Get an Informational Listing from Spamhaus

It’s now very common for the most powerful blocklist operator, Spamhaus, to issue what’s called an “informational listing” before formally blocklisting a sender. These informational listings don’t have any immediate impact, but they’re a warning that a formal listing is likely to happen if you don’t take action. So, take them seriously.

When to Call In Expert Help

Experiencing any of those events could and probably should prompt you to reach out for some help from a deliverability expert. Better safe than sorry is the name of the game when it comes to deliverability, given the costs associated with email deliverability problems. 

For example, before becoming a client of ours, a national retailer was having problems at just Yahoo and AOL and it was costing them $100,000 a week in lost email sales. If your brand has suffered deliverability issues in the past that have led to this level of lost revenue, or if your brand generates millions of dollars from email marketing every year, then my answer for when to seek expert deliverability help is different for you: 

You should have deliverability help all the time.

Brands with smaller financial risks can manage their deliverability reactively, calling in help when problems arise. But for you, the potential losses associated with deliverability problems are simply so high that they must be managed proactively. 

At a minimum, someone in your organization should be reviewing the key deliverability performance metrics and they should understand when to take action. However, we often find that even if a brand has a resident deliverability expert, it’s not a full solution. Because these employees often serve other roles and have other responsibilities in addition to deliverability, it almost always makes sense to also have an ongoing partnership with an external deliverability consultant to protect your email reputation and manage performance.

Unfortunately, if you’re not watching it all the time for trouble, it doesn’t take long to ruin your deliverability. And once your reputation is damaged, it can take a while to rehabilitate it. It boils down to the simple fact that without good deliverability, nothing else matters, because your subscribers aren’t seeing your emails.

The on-going review and assessment of your email program from a deliverability perspective is smart insurance for all the money you’re investing in email marketing. It gives you the peace of mind that your key performance indicators are in the green, and that you are trending in the right direction month-over-month, and year-over-year. If an issue crops up because of one of the 13 issues listed above, you will know there is someone to help you minimize the damage as quickly as possible.


 Need help with your email deliverability? Oracle Digital Experience Agency has hundreds of marketing and communication experts ready to help Oracle customers create stronger connections with their customers and employees, even if they’re not using an Oracle platform as the foundation of that experience. Our award-winning specialists can handle everything from creative and strategy to content planning and project management. For example, our full-service email marketing clients generate 24% higher open rates, 30% higher click rates, and 9% lower unsubscribe rates than Oracle Responsys customers who aren’t.

For help overcoming your challenges or seizing your opportunities, talk to your Oracle account manager, visit us online, or email us at OracleAgency_US@Oracle.com.

Want to better understand your email marketing risks and opportunities, take advantage of our free Email Marketing Assessment. Our experts will check your deliverability, review your email creative, audit your signup process, do a partial competitive analysis, and more. If interested in this free assessment, reach out to us at OracleAgency_US@Oracle.com.

Now thoroughly updated, this blog post was originally published on July 30, 2019 by Clea Moore. 

Daniel Deneweth

Head of Email Deliverability Services, Oracle Digital Experience Agency

Daniel Deneweth heads up a team of Email Deliverability Services team at Oracle Digital Experience Agency. He shows clients how to maximize the ROI from email through improved inbox placement. Prior to Oracle, Daniel held a variety of roles at the deliverability firm Return Path. His tenure included managing the Sender Score Certified program, where he collaborated with ISPs and helped senders implement email best practices. Daniel brings this insight and in-depth deliverability knowledge to help clients maximize their inbox placement rates, and accelerate the ROI of their email channel.

Previous Post

10 Years of Email Marketing Rules: What’s Changed & What’s Next [on-demand webinar]

Chad S. White | 3 min read

Next Post

AI-Generated Images: Generative AI Concerns & Opportunities for Marketers

Meghan Flynn | 7 min read