How to improve welcome series email deliverability and reduce fake sign-ups?
Michael Ko
Co-founder & CEO, Suped
Published 26 Jul 2025
Updated 19 Aug 2025
8 min read
Seeing your welcome series email deliverability dip can be a frustrating experience, especially when you suspect it is due to fake sign-ups. It's a common challenge that impacts everything from open rates to your overall sender reputation. A gradual decline, even if it seems small initially, can signal underlying issues that need prompt attention.
The welcome series is often the first interaction a new subscriber has with your brand, making its deliverability critically important. If these initial emails land in spam or bounce, it not only wastes sending resources but also sets a negative precedent for future communications, potentially leading to long-term deliverability problems.
The hidden costs of invalid sign-ups
Fake sign-ups, whether from bots, malicious actors, or users providing incorrect details, pose a significant threat to email deliverability. These invalid addresses can lead to high bounce rates, which internet service providers (ISPs) view as a strong negative signal, indicating poor list quality or potentially spammy sending practices.
When your bounce rate spikes, particularly for initial emails to new users, it can flag your sending domain as suspicious. This can result in your emails being directed to the spam folder, or even blocked entirely, impacting not just your welcome series but your entire email program. For a deeper understanding of how these issues affect your email reputation, consider reviewing a guide on how to improve your email reputation. how to improve your email reputation.
Beyond bounce rates, fake sign-ups also dilute your engagement metrics. If a significant portion of your list consists of unengaged or invalid addresses, your open and click-through rates will naturally suffer. ISPs interpret low engagement as a sign that your content is not valuable, further degrading your sender reputation.
A continuous drop in deliverability, even if it's small, indicates a systemic problem. It is not just about the numbers; it is about maintaining a healthy relationship with mailbox providers and ensuring your messages reach legitimate inboxes.
Fortifying your signup forms
The most effective way to combat fake sign-ups is to implement robust preventative measures on your signup forms. This ensures that only genuinely interested subscribers with valid email addresses make it onto your list. Here are some key strategies I recommend:
Implementing CAPTCHA or reCAPTCHA
Adding a CAPTCHA or reCAPTCHA challenge to your forms is a fundamental step. This helps distinguish between human users and automated bots, significantly reducing the volume of fraudulent sign-ups. Many providers offer invisible reCAPTCHA options that minimize user friction.
Leveraging double opt-in
Double opt-in requires new subscribers to confirm their subscription by clicking a link in a confirmation email. This process is highly effective in filtering out fake or mistyped email addresses and ensures that subscribers genuinely want to receive your communications. For more details on the benefits of double opt-in, you can refer to an article on double opt-in strategies.
Real-time email validation
Integrating a real-time email validation service or library into your signup forms can catch invalid email addresses at the point of entry. Tools like MailCheck can help correct typos and flag obviously malformed addresses. For more sophisticated checks, an API-based validation service can provide real-time data-driven insights into email validity, including identifying disposable email signups. disposable email signups. Here is an example of what basic client-side validation logic might look like, similar to what MailCheck offers:
Basic Email Validation Examplejavascript
function validateEmail(email) {
var re = /^(([^<>()\[\]\\.,;:\s@\"]+(\.[^<>()\[\]\\.,;:\s@\"]+)*)|(\".+\"))@((\[[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\])|(([a-zA-Z\-0-9]+\.)+[a-zA-Z]{2,}))$/;
return re.test(String(email).toLowerCase());
}
Offer incentives behind email verification
If you offer a free week or a coupon, consider delivering it via email after signup. This compels users to provide a real, active email address if they want to claim the offer, naturally filtering out many fake or inactive accounts. This approach significantly improves your list quality from the start.
These measures can be combined for even greater security and list hygiene. You can learn more about how to implement these strategies to prevent nefarious email signups.
Staying ahead with monitoring and segmentation
Even with preventative measures in place, ongoing monitoring and a proactive response to deliverability issues are essential. This helps you identify problems early and prevent them from escalating.
Monitoring key deliverability metrics
Regularly check your email metrics, especially for your welcome series. Pay close attention to open rates, click-through rates, and bounce rates, ideally segmented by domain.
Open rates by domain: If you see a significant discrepancy (e.g., your overall open rate is 15%, but for gmail.com it's 2%), this indicates a specific deliverability problem with that particular domain. The same applies to yahoo.com, which has recently implemented tighter sending requirements. You can read more about new deliverability updates from major mailbox providers.
Delivery rates by domain: A low delivery rate for a specific domain might mean it is blocklisting (or blacklisting) your mail due to an unnoticed issue. This is different from bounces, as it indicates a more severe rejection.
Spam trap hits: Spam traps are email addresses used by ISPs to identify spammers. Hitting them indicates a problem with your list hygiene, often a sign of fake sign-ups or old, unengaged contacts. Knowing how to avoid spam traps is crucial for maintaining good sender reputation.
Automated bounce management
Set up automations to immediately unsubscribe or suppress contacts who hard bounce on the first email of your welcome series. This prevents continued sending to invalid addresses, which can further damage your sender reputation. For instance, if an email to example@gmail.com bounces, automatically remove it from your active list.
Why timely list cleaning matters
Regularly cleaning your email list is not just a best practice, it's a necessity. Removing inactive or invalid addresses reduces your bounce rate, minimizes the risk of hitting spam traps, and improves overall engagement metrics. This proactive approach helps maintain a healthy sender reputation and ensures your campaigns reach interested recipients.
Reduced bounce rates: Lower hard bounce rates signal better list quality to ISPs.
Improved sender reputation: A clean list leads to higher engagement and better inbox placement.
Lower costs: Avoids paying for sending emails to invalid addresses.
For specific issues, like a subscription bombing attack, it is essential to have strategies in place to recover and improve transactional email deliverability. improve transactional email deliverability.
Crafting an engaging welcome journey
While preventing fake sign-ups is crucial, the content and structure of your welcome series also play a significant role in deliverability. Even legitimate subscribers may disengage if the welcome experience is not optimized.
Optimizing welcome series length and cadence
Mailbox providers, like Gmail, are sensitive to how many emails new recipients receive, especially if they are not opening or clicking. I have found that a welcome series of 3-4 sends tends to be optimal for new recipients. Sending too many emails too quickly can lead to disengagement and increased spam complaints, hurting your sender reputation.
Content relevance and engagement
Ensure your welcome emails are highly relevant and provide immediate value. Personalize content where possible and include clear calls to action. Engaged subscribers are less likely to mark your emails as spam, which directly improves your deliverability. If your welcome emails are going to spam, analyzing your content and engagement is a critical step.
Consider implementing strategies that improve deliverability for B2C onboarding flows, particularly when dealing with a high volume of Gmail addresses. This often involves ensuring strong sender authentication and positive engagement signals.
Views from the trenches
Best practices
Implement double opt-in for all new sign-ups to verify email authenticity and user intent.
Utilize CAPTCHA or reCAPTCHA on all signup forms to deter automated bot submissions.
Integrate real-time email validation at the point of entry to catch invalid or misspelled addresses instantly.
Ensure your welcome series is concise, typically 3-4 emails, and focuses on delivering immediate value to new subscribers.
Segment your audience and personalize welcome content to improve engagement and reduce the likelihood of spam complaints.
Common pitfalls
Relying solely on single opt-in without additional fraud prevention, leading to high fake sign-up rates.
Not monitoring deliverability metrics, like bounce rates by domain, in real time.
Sending overly long or frequent welcome series emails to new, unengaged subscribers.
Failing to automatically unsubscribe or suppress contacts who hard bounce on initial emails.
Ignoring low open rates or high spam complaints, especially for specific mailbox providers.
Expert tips
Consider offering valuable incentives (like free trials or discounts) only after email verification has occurred.
Regularly audit your email list for inactive or unengaged subscribers and remove them to maintain list hygiene.
Use domain-specific open rate analysis to pinpoint and address deliverability issues with particular ISPs.
Implement a system to analyze signup patterns for signs of programmatic activity, such as repetitive name formats (e.g., '0001@').
Leverage DMARC reports to gain insights into your authentication status and delivery performance across various mailbox providers.
Marketer view
A marketer from Email Geeks says that checking year-over-year performance can help determine if a dip in deliverability is seasonal or a deeper issue.
2019-05-15 - Email Geeks
Expert view
An expert from Email Geeks says that having CAPTCHA in place and focusing on engaged customers are key strategies.
2019-05-15 - Email Geeks
Building a foundation for successful email engagement
Improving welcome series deliverability and reducing fake sign-ups requires a multi-faceted approach. By combining robust form security, proactive monitoring of key metrics, and strategic optimization of your welcome content, you can build a healthier email list and ensure your critical first impressions land where they belong: the inbox.
It is an ongoing process that involves continuous vigilance and adaptation, but the benefits, including higher engagement, better sender reputation, and ultimately, more effective marketing campaigns, are well worth the effort.
gmail.com it's 2%), this indicates a specific deliverability problem with that particular domain. The same applies to 
yahoo.com, which has recently implemented tighter sending requirements. You can read more about new deliverability updates from major mailbox providers.
Gmail, are sensitive to how many emails new recipients receive, especially if they are not opening or clicking. I have found that a welcome series of 3-4 sends tends to be optimal for new recipients. Sending too many emails too quickly can lead to disengagement and increased spam complaints, hurting your sender reputation.
