Troubleshooting
Common causes of SMTP auth failures for application mail—credentials, ports, TLS, and provider policies.
Verify username, password or API tokens, and that the mailbox allows SMTP submission from your IP ranges.
Prefer STARTTLS or implicit TLS on the ports your provider documents—mixed modes often fail with modern servers.
Burst sending can trigger temporary blocks—reduce concurrency and monitor provider dashboards.
Why DNS changes lag, how TTL affects rollout, and how to verify TXT records globally.
DMARC can pass while folders still filter mail—check reputation, content signals, and mailbox-specific filters.
Why multiple SPF TXT strings break validation and how to merge includes into a single record.
TXT and CNAME entries for SPF, DKIM, and DMARC when Cloudflare proxies email-related names correctly.
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