Email delivery depends on authentication, sending behaviour and reputation as well as mailbox configuration. Reseller environments may also enforce hourly or per-domain sending limits.
Step by step
- Ensure customer domains have correct SPF and DKIM and encourage DMARC once legitimate senders are known.
- Use authenticated SMTP for applications rather than unauthenticated or spoofed sending.
- Keep mailing lists permission-based and remove invalid addresses.
- Investigate bounce messages instead of repeatedly resending.
- Monitor compromised scripts/mailboxes because spam can damage shared reputation.
Important
Hosting email is not a substitute for a specialist bulk-marketing platform. Large campaigns can exceed server limits and affect other users.
Checks and troubleshooting
For a delivery complaint, obtain the full bounce/rejection message, sending domain, recipient domain and approximate time. “It went to spam” alone is not enough to diagnose.