Why your OTP emails go to spam

Short Answer

Spam placement is rarely caused by one magic word in the template. Receivers look at whether the sender is authenticated, whether the authenticated domain matches the visible sender, how recipients react, whether addresses bounce, and whether your traffic pattern looks normal.

1. Check SPF, DKIM, And DMARC

Authentication is the first gate. If your OTP message cannot prove who sent it, inbox providers have little reason to trust it.

• SPF exists at the sending domain and includes every service that sends OTP mail.
• DKIM is enabled for the provider that signs your OTP messages.
• DMARC exists at _dmarc.yourdomain.com and can receive reports through rua.
• The visible From: domain aligns with either the SPF domain or the DKIM signing domain.
• There is only one SPF TXT record. Multiple SPF records can make SPF fail.

For transactional OTP, DKIM alignment is often the most reliable path because SPF can break when mail is forwarded. Do not stop at DNS existence; inspect the actual delivered message headers and confirm pass results.

2. Separate Transactional Mail

OTP email should not ride on the same reputation as newsletters, cold outreach, product announcements, or lifecycle campaigns. A user who marks a promotion as spam should not hurt passwordless login.

3. Make The Message Boring

OTP messages should be short, plain, and easy to classify. The receiver should see a transactional security message, not a campaign.

• Use a direct subject such as Your example.com verification code.
• Include both HTML and plain text bodies.
• Put the code near the top of the message.
• Include the purpose, expiration, and a line for users who did not request the code.
• Use full links on your domain. Avoid URL shorteners and unrelated tracking domains.
• Keep images optional. The message should make sense with images blocked.

Subject: Your example.com verification code

Your verification code is 493021.

It expires in 10 minutes. If you did not request this code,
you can ignore this email.

4. Inspect Reputation Signals

A technically valid message can still go to spam if receivers see bad reputation. For OTP, the most common reputation problems are fake signups, repeated sends to bad addresses, complaint spikes, and sudden volume changes.

• Log hard bounces and stop sending to addresses that do not exist.
• Watch soft bounces and deferrals during provider incidents or rate limiting.
• Track complaint feedback loops where your provider supports them.
• Warm up new domains and sender identities gradually.
• Throttle resend buttons so one user cannot create a burst of identical mail.
• Filter disposable, malformed, or obviously abusive addresses before sending.

5. Check The OTP Flow Itself

Deliverability and product state are connected. A resend loop can create unnecessary email volume, trigger rate limits, and teach users to keep clicking.

Make resend idempotent: the same email and purpose should get the same active code for the TTL. That reduces support churn and avoids turning one login attempt into five different messages.

6. Read A Real Delivered Header

Send one OTP to a Gmail or Yahoo inbox you control, open the original message, and inspect the authentication results. You are looking for pass results and aligned domains, not just DNS records that look right in a dashboard.

Authentication-Results:
  spf=pass smtp.mailfrom=bounces.auth.example.com;
  dkim=pass header.d=auth.example.com;
  dmarc=pass header.from=example.com;

If DMARC fails while SPF or DKIM passes, you likely have an alignment problem. The provider may be authenticating its own bounce domain or DKIM domain, while the visible From domain is yours.

The Quick Diagnostic Checklist

• DNS has valid SPF, DKIM, DMARC, and MX records.
• Delivered headers show SPF or DKIM pass and DMARC pass.
• The visible From domain aligns with SPF or DKIM.
• The sender identity is consistent and transactional-only.
• The OTP template has both text and HTML versions.
• The message has no promotional content, URL shorteners, or unrelated tracking domains.
• Bounces, suppressions, and complaint signals are logged.
• Send and resend endpoints are rate-limited.
• New sender domains are warmed up instead of launched at full volume.

FAQ