Why your cold email is going to spam: a diagnostic checklist
Six common causes, in order of frequency, with the dig commands to confirm each one.
Rejwan Nirob·Dec 28, 2025·7 min readSpam folder placement has many causes. Most are infrastructure - half of the cold-email spam-folder problems we see in support are SPF, DKIM, or DMARC misconfiguration. Here is the diagnostic order.
1. SPF check
Run dig +short yourdomain.com TXT and look for v=spf1. Confirm exactly one record. Confirm the include matches your sender (Workspace: include:_spf.google.com). Two records is a silent failure.
2. DKIM check
Run dig +short google._domainkey.yourdomain.com TXT. Confirm the public key is published, 2048-bit, with no truncation. Send a test email to mail-tester.com and verify the DKIM signature column shows pass.
3. DMARC check
Run dig +short _dmarc.yourdomain.com TXT. Confirm the record exists. Confirm p=quarantine or p=reject. Confirm aspf=r and adkim=r unless you have a specific reason for strict alignment.
4. List quality
Hard-bounce rate above 4% will land mail in spam regardless of infrastructure. Run the list through a verification service (ZeroBounce, MillionVerifier) and remove invalid addresses.
5. Content patterns
Spam-trigger phrasing, image-only emails, suspicious links, link shorteners - these all bias placement toward spam. Plain text with a single link to your real domain is the safest baseline.
6. Volume curve
A mailbox jumping from 5 messages on day 7 to 40 messages on day 8 will land in spam. Stick to the warmup ramp. Cap at 10 to 20 per day after warmup completes - well below the platform ceiling.
Send a test from your mailbox to mail-tester.com. The score is graded on every layer above. A 9.5/10 or higher is healthy. Below 8 means something is wrong.
Frequently asked
Why is my cold email going to spam?
Six common causes in order of frequency: (1) broken or duplicate SPF record, (2) missing or weak DKIM, (3) missing DMARC, (4) hard-bounce rate above 4%, (5) spam-trigger phrasing or image-only emails, (6) sudden volume jumps that violate the warmup ramp. Half of spam-folder issues are SPF/DKIM/DMARC misconfiguration.
How do I check my SPF record?
Run dig +short yourdomain.com TXT and look for v=spf1. Confirm exactly one record. Confirm the include matches your sender (Workspace: include:_spf.google.com). Two SPF records is a silent failure that tanks DMARC alignment.
How do I check if DKIM is set up correctly?
Run dig +short google._domainkey.yourdomain.com TXT. Confirm the public key is published, 2048-bit, with no truncation. Then send a test email to mail-tester.com and verify the DKIM signature column shows pass. Below 9.5/10 on mail-tester usually means something is wrong.
Can content alone send cold email to spam?
Yes, but it is rarely the only cause. Spam-trigger phrasing, image-only emails, suspicious links, link shorteners, or all-caps subject lines all bias placement toward spam. Plain text with a single link to your real domain is the safest baseline. Fix infrastructure first, then iterate on copy.