In this article, we look at essential tips and techniques to protect your list from spam traps, bot attacks, and other challenges, ensuring an effective email marketing strategy.
Comparing single opt-in to double opt-in
While double opt-in (DOI) is the widely recommended practice for email subscription, understanding its pros and cons can help you make an informed decision about whether or not to use single opt-in instead.
Double opt-in pros and cons
Pros:
Double opt-in (DOI) is the only definitive way to confirm at the point of collection that:
the email address is valid.
the owner of the inbox is the person subscribing.
the owner of the inbox consents to receiving emails.
It prevents spam traps from being intentionally or accidentally added to lists, which can cause blocklistings.
It prevents abusive bots from adding contacts to lists.
Cons:
Conversion for DOI requires an additional step, resulting in a smaller list.
Maintaining and improving conversion rate requires resources to create/test content.
When to choose double opt-In
Although double opt-in (DOI) is not legally mandated in many regions, it is considered best practice for every sender.
Senders are highly encouraged to use double opt-in (DOI), especially if they:
have previously or are currently experiencing deliverability problems.
have been flagged for compliance violations for hitting spam traps or causing blocklistings.
have been or are a target for bad actors; for example, revenge spam, bot attacks on forms, polarising views.
use personalisation in their welcome email series, which could be hijacked for phishing.
incentivise sign-ups, such as to win a prize.
German mailbox providers, such as t-online.de, require proof of DOI to mitigate delivery/deliverability challenges.
Read more about power of double opt-in in our blog The power of double opt-in (DOI) for email deliverability.
Ways to strengthen single opt-in security
While double opt-in is an effective method for maintaining a clean email subscription list, many marketers run the risk of trying to build as large a list as possible and maximize potential revenue.
To protect themselves from the risks associated with not using double opt-in, senders implementing single opt-in should seriously consider the following measures:
1. CAPTCHA or reCAPTCHA
Implement CAPTCHA or Google's reCAPTCHA on your subscription forms to prevent less sophisticated spam bots from submitting fake sign-ups. Be aware that more advanced bots can bypass CAPTCHA, and manual completion of CAPTCHAs is possible with sufficient incentive.
2. Form validation
Use widely available field validation tools to ensure users provide correctly formatted email addresses. Require users to enter their email address twice to minimise typos.
3. Honeypot fields
Add human-invisible fields to your subscription form that only bots can see. If these fields are filled upon form submission, it's likely an illegitimate submission, allowing you to ignore or filter out the response.
4. IP restrictions
Block, restrict, or rate limit form submissions based on the submitting IP address. Consider preventing submissions from IPs in high-risk countries or those where you don't do business. Restrict multiple submissions from the same IP address and implement a minimum time delay for form submissions to deter malicious bots.
5. Welcome email
Send a welcome email after users subscribe, informing them of a successful subscription and providing an immediate unsubscribe option for mistaken sign-ups. Suppress any contacts where the welcome email, hard or soft, bounces.
6. Track sources
Record all contact sources, enabling easy identification and segmentation based on the source. This helps narrow down the search and remove only affected contacts in case of subscription form abuse. If all forms filter into one list with no source differentiator and you end up with spamtraps or worse on your list, you risk losing legitimate contacts in order to de-risk the list.
7. List hygiene
Implement ongoing list hygiene to identify unengaged contacts, attempt re-engagement, reduce sending frequency for less engaged contacts, and sunset contacts unlikely to re-engage and generate revenue. Accelerate this process for contacts that do not engage with your welcome series and come through a single opt-in source.