Why Gmail rejects your emails
Gmail uses multiple signals to decide whether to accept, reject, or spam-filter your emails. Authentication failures, blacklist listings, and poor sender reputation are the most common causes. Understanding each helps you fix deliverability problems systematically.
Missing SPF or DKIM
Gmail expects every sending domain to publish a valid SPF record and sign outgoing emails with DKIM.
Without SPF, Gmail cannot verify that the sending server is authorised. Without DKIM, Gmail cannot verify message integrity. Missing either increases the spam score Gmail assigns to your messages.
Since February 2024, Google enforces stricter requirements for bulk senders: SPF and DKIM must both be configured correctly. Failing these requirements can cause rejection or spam placement.
DMARC alignment failures
DMARC adds a policy layer above SPF and DKIM. Gmail checks whether the authenticated domain aligns with the visible From: header domain.
If neither SPF nor DKIM passes with alignment, DMARC fails. With a DMARC policy of p=quarantine or p=reject, Gmail will move the message to spam or reject it at the SMTP level.
Common DMARC alignment failures include: SPF passing at the envelope level but the MAIL FROM domain not matching the From: header, or DKIM signing with a domain that does not align with the From: domain.
Blacklist and reputation problems
Gmail checks sending IP addresses against DNS blacklists and maintains its own internal reputation database.
If your sending IP is listed on a major DNSBL such as Spamhaus ZEN, Gmail may reject or spam-filter your messages.
Even without a blacklist listing, a domain with high bounce rates, frequent spam complaints, or a history of sending to invalid addresses builds a poor reputation that causes Gmail to treat messages as spam.
New IPs and new domains have no established reputation. Gmail applies stricter filtering during the warmup period.
Gmail spam filtering signals
Gmail's spam filter uses many signals beyond authentication:
User engagement. If recipients rarely open or interact with your emails, or if they move them to spam, Gmail lowers your sender score.
Content quality. Misleading subject lines, excessive links, spam-trigger phrases, invisible text, and malformed HTML increase spam scores.
Unsubscribe compliance. Bulk senders must include a one-click unsubscribe option and honour unsubscribe requests within two days.
List hygiene. Sending to unverified, purchased, or harvested lists generates hard bounces and complaints that damage reputation.
SMTP TLS and transport security
Gmail expects receiving and sending mail servers to support STARTTLS for encrypted mail transport.
If your outbound mail server does not support TLS, Gmail may log the connection as insecure. TLS certificate errors or expired certificates can also reduce trust.
Configuring MTA-STS enforces TLS for inbound mail and signals that your domain takes transport security seriously.
How to troubleshoot Gmail deliverability
Start by checking SPF, DKIM, DMARC, MX, blacklists, SMTP TLS, and MTA-STS for your domain.
Use Google Postmaster Tools to monitor your domain and IP reputation as seen by Gmail. Postmaster Tools shows spam rates, delivery errors, and authentication results.
Run the MXFend Email Security Score for a single-report view of all authentication, blacklist, and transport security issues.
Frequently asked questions
Why does Gmail send my emails to spam?
Common causes include missing SPF or DKIM, DMARC alignment failures, blacklist listings, poor sender reputation, and content that triggers Gmail's spam filters.
Does SPF help Gmail deliverability?
Yes. A valid SPF record allows Gmail to verify that your sending server is authorised. Missing or broken SPF increases spam scores and can cause Gmail to reject or spam-filter messages.
Can blacklists affect Gmail inbox placement?
Yes. Gmail checks sending IPs against DNS blacklists. A blacklist listing can cause Gmail to reject messages or route them to spam.
How do I test email deliverability?
Run the MXFend Email Security Score to check SPF, DKIM, DMARC, blacklist status, SMTP TLS, and more. Also use Google Postmaster Tools to monitor Gmail-specific reputation and delivery data.