Error Codes Library – Gmail/Google Workspace

Overview

When sending emails through Gmail or Google Workspace in PXME, you may encounter SMTP (Simple Mail Transfer Protocol) error codes. These codes explain why an email failed to deliver and guide you toward the right fix.

This library organizes common Gmail/Google Workspace error codes, their meaning, and troubleshooting steps for faster resolution.

Common Error Categories

400-Level Errors (Temporary Issues)

• 421 “4.3.0” / “4.7.0” → Temporary system problem or server busy.
  Fix: Retry sending later.

• 421 “4.7.0” IP not in whitelist → Sending IP not authorized.
  Fix: Check sending IP permissions.

• 421 “4.7.0” Unusual rate of unsolicited mail → Too many spam-like sends.
  Fix: Review email practices; follow Gmail sender guidelines.

• 450 “4.2.1” → User receiving too quickly / quota exceeded.
  Fix: Retry later, reduce sending speed.

• 451 “4.3.0 / 4.5.0” → SMTP protocol violation or multiple domains in one transaction.
  Fix: Correct SMTP setup; send per-domain.

• 452 “4.2.2” → Recipient mailbox over quota.
  Fix: Ask recipient to clear space.

• 454 “4.7.0” → Authentication issues.
  Fix: Retry; check credentials; enable STARTTLS if required.

500-Level Errors (Permanent Failures)

• 501 “5.5.x” → Syntax or decode errors.
  Fix: Check formatting, SMTP commands, HELO/EHLO arguments.

• 502 “5.5.1” → Too many unrecognized commands / unimplemented command.
  Fix: Correct SMTP usage.

• 503 “5.5.1” → EHLO/MAIL/RCPT not in correct order.
  Fix: Follow SMTP sequence.

• 504 “5.7.4” → Unrecognized authentication type.
  Fix: Update authentication method.

• 530 “5.5.1 / 5.7.0” → Authentication required / STARTTLS required.
  Fix: Provide valid credentials and enable TLS.

• 535 “5.7.1” → Authentication error (password, 2FA, invalid credentials).
  Fix: Use correct username/password; create App Password if 2FA enabled.

• 550 “5.1.1” → Recipient address doesn’t exist.
  Fix: Check for typos.

• 550 “5.2.1” → Recipient disabled or over quota.
  Fix: Contact recipient another way.

• 550 “5.4.5” → Daily quota exceeded.
  Fix: Stay under Gmail/Workspace limits or upgrade plan.

• 550 “5.7.1” → Unauthenticated, relay denied, unusual activity.
  Fix: Ensure SPF, DKIM, and DMARC are correct.

• 550 “5.7.26” → DMARC/SPF/DKIM failure.
  Fix: Correct domain authentication records.

• 552 “5.2.x” → Over quota or message too large.
  Fix: Reduce size; remove large attachments.

• 553 “5.1.2” → Recipient domain not found.
  Fix: Double-check domain spelling.

• 554 “5.6.0 / 5.7.0” → Malformed message, security issue, or blacklisted IP.
  Fix: Review content, attachments, IP reputation.

• 555 “5.5.x / 5.7.1” → Authentication or syntax error.
  Fix: Verify credentials and email structure.

Pro Tips for Troubleshooting

1. Check Authentication First

• Ensure SPF, DKIM, and DMARC are configured for your sending domain.

• If using Gmail with PXME and 2FA is enabled, set up App Passwords.

2. Monitor Sending Limits

• Gmail: 500 emails/day.

• Google Workspace: 2,000 emails/day (varies by edition).

• Avoid exceeding to prevent lockouts.

3. Content Quality Matters

• Avoid spammy keywords, excessive links, oversized attachments.

• Follow Gmail’s bulk sender guidelines.

4. Use PXME’s Email Analytics

• Track bounces, complaints, delivery issues.

• Re-engage or remove inactive/bounced contacts.

5. Escalate if Needed

• For persistent issues, contact your DNS host or Google Workspace admin.

Quick Reference: Most Common Gmail Errors in PXME

• 535 5.7.1 → Wrong password / App Password required.

• 550 5.7.26 → DMARC/SPF/DKIM authentication failed.

• 550 5.1.1 → Email address doesn’t exist.

• 550 5.4.5 → Daily sending quota exceeded.

• 421 4.7.0 → Gmail flagged unusual sending activity (spam-like).