You spot it in your Klaviyo dashboard: dozens of new signups, all variations of the same Gmail address. One subscriber becomes [email protected], [email protected], and fifteen other random combinations. This isn’t enthusiasm for your newsletter—it’s a coordinated attack on your email list.
The Real Prize: Your Validated Email Data
Bots don’t want your marketing emails; they want proof your system accepts signups.
These automated signups serve a darker purpose than inbox clutter. Bots testing your signup forms with Gmail plus variations are actually validating that the base email address is active and responsive. Once confirmed, that validated email becomes a sellable commodity on underground markets. Your signup process essentially becomes an email verification service for spammers, phishers, and scammers who monetize clean contact lists.
Successful bot signups grant access to your entire email stream. Automated systems can analyze your campaign patterns, test your links for vulnerabilities, and map your marketing funnel structure—intelligence that benefits competitors or enables more sophisticated attacks later.
Why Plus Addressing Screams “Bot”
Gmail treats all plus variants as identical, making mass signups statistically impossible for real users.
The Gmail plus trick exploits a fundamental gap in most email systems. While [email protected] and [email protected] appear as separate addresses to your database, Gmail delivers both messages to the same [email protected] inbox. Real users occasionally add meaningful identifiers like [email protected] for organization, but random character strings serve no human purpose.
Bots leverage plus addressing to circumvent your duplicate signup protection. Your system blocks the same email from registering twice, but these plus variants slip through as “different” addresses while targeting the same inbox.
Lock Down Your Signup Forms
CAPTCHA challenges stop automated signups before they pollute your list.
The most effective defense happens at the gate. CAPTCHA verification creates a human-versus-machine checkpoint that eliminates bot signups with minimal friction for legitimate users. Honeypot fields—hidden form elements that humans can’t see but bots auto-fill—provide another automated detection layer.
Double opt-in confirmation emails stop most bot operations cold. Bots often lack access to the target inbox or can’t reliably click confirmation links, so this two-step process naturally filters automated signups while ensuring genuine subscriber intent.
Monitor your signup patterns for clustering red flags:
- Multiple plus-addressed variations from the same base email
- Rapid-fire submissions from identical IP addresses
- Nonsensical character combinations in the identifier portion
Your email marketing ROI depends on genuine engagement, not inflated subscriber counts that tank your sender reputation with every campaign.
