Error: sendgrid emails going to spam

"SendGrid emails going to spam" is not an SMTP error code and SendGrid does not have a "send to spam" setting. SendGrid almost always accepts your message (returns a 250 success) and relays it to the recipient's mail server. The decision to file it under Spam/Junk is made afterward, by the receiving provider's filters (Gmail, Yahoo, Microsoft 365/Outlook), based on authentication, sender reputation, recipient engagement, and content. So fixing this means improving the signals those filters score — not changing anything in SMTP.

What causes SendGrid emails to go to spam?

The receiving inbox distrusts the message. The most common, source-backed reasons:

• Incomplete domain authentication. If SPF, DKIM, and DMARC don't pass and align to your domain, Gmail and Yahoo treat the mail as unverified. As of February 2024, Gmail and Yahoo require bulk senders (5,000+ messages/day to their users) to have SPF, DKIM, and DMARC; Google escalated to permanent rejections in late 2025.
• No one-click unsubscribe. Bulk senders must include RFC 8058 List-Unsubscribe and List-Unsubscribe-Post headers, or messages are filtered.
• High spam-complaint rate. Google requires the rate in Postmaster Tools to stay below 0.3%, and recommends below 0.10%. Above 0.3%, spam-folder placement and rejections spike.
• Poor/cold IP reputation. On a dedicated IP that wasn't warmed up (or is idle 30+ days), or a shared IP harmed by other senders, ISPs distrust the source.
• Weak engagement or spammy content. Low opens, stale lists, purchased lists, spam-trigger phrasing, broken links, or image-heavy/no-text-balance mail lower placement.

How do I fix SendGrid emails going to spam?

Work top-down — authentication first, it's the highest-leverage fix:

1. Complete SendGrid Domain Authentication. In SendGrid: Settings → Sender Authentication → Authenticate Your Domain. With Automated Security on (default), SendGrid generates three CNAME records (one for mail, two for link branding) plus a DMARC TXT record; add them at your DNS host and click Verify (allow up to 48h). This sets up DKIM and SPF aligned to your domain and removes the "via sendgrid.net" tag.
2. Publish a DMARC record. Add a TXT record at _dmarc.yourdomain.com, starting at monitoring before tightening:

   1
   _dmarc.yourdomain.com  TXT  "v=DMARC1; p=none; rua=mailto:dmarc@yourdomain.com"
   

   Confirm reports show SPF/DKIM passing and aligned, then move toward p=quarantine/p=reject.
3. Add one-click unsubscribe (RFC 8058) on bulk mail. SendGrid's Subscription Tracking adds compliant List-Unsubscribe / List-Unsubscribe-Post: List-Unsubscribe=One-Click headers automatically — enable it under Settings → Tracking.
4. Drive your complaint rate below 0.3% (target <0.1%). Use double opt-in, suppress unengaged recipients, never send to purchased lists, and monitor Google Postmaster Tools plus SendGrid's Engagement Quality/Spam Reports.
5. Warm up a dedicated IP. If you use a dedicated IP, enable SendGrid's automatic IP warmup so volume ramps gradually; re-warm any IP idle 30+ days. (Free/Essentials shared pools don't need this.)
6. Diagnose a specific message. Open the message's full headers (Gmail's "Show original") and check the Authentication-Results line for spf=pass, dkim=pass, dmarc=pass. Use a tool like mail-tester.com to score content and check the sending IP against Spamhaus.

If you route through Courier to SendGrid, the same DNS authentication applies to your sending domain — configure SendGrid domain authentication once, and Courier's SendGrid provider will send authenticated mail.