SMTP errors in Senddera usually appear in sending logs, failed queue jobs, or a test-email popup. Fix them by verifying host, port, encryption, credentials, and firewall/DNS — in that order.
Connection settings reference
| Provider pattern | Host | Port | Encryption |
|---|---|---|---|
| TLS (recommended) | smtp.example.com | 587 | TLS / STARTTLS |
| SSL (legacy) | smtp.example.com | 465 | SSL |
| Amazon SES | email-smtp.REGION.amazonaws.com | 587 | TLS |
| Plain (rare, insecure) | — | 25 | None — often blocked on VPS |
Detailed SES setup: Configuring Amazon SES.
Step 1 — Test from the server
SSH to the Senddera host and test reachability:
nc -zv email-smtp.us-east-1.amazonaws.com 587
# or
openssl s_client -connect smtp.example.com:587 -starttls smtpIf Connection refused or timeout:
- Cloud provider blocking outbound 25/587 — open in security group or use provider SMTP
- Wrong hostname or region (SES region must match endpoint)
Step 2 — Credentials and auth
- Username/password — SES uses SMTP credentials from IAM, not console password
- API keys — some drivers use API instead of SMTP; match the driver type in Senddera
- 2FA apps — Google Workspace may need app passwords
- Rotate credentials and update Sending Server; then
php artisan queue:restart
Step 3 — TLS / certificate errors
Errors like certificate verify failed or SSL routines:
- Ensure server CA bundle is current:
sudo apt-get install ca-certificates - Do not disable TLS verification in production
- Clock skew — sync NTP (
timedatectl)
Step 4 — Senddera sending server form
Admin → Sending → Sending Servers → edit server:
- Match encryption dropdown to port (587 + TLS, 465 + SSL)
- Set From email to a verified domain/address (SES, SendGrid)
- Run Test connection if available
- Assign server to customer / mail list as needed
Step 5 — SPF/DKIM and bounces (after connect works)
SMTP success does not guarantee inbox placement. Configure SPF, DKIM, DMARC and monitor bounces via feedback loops.
Common error messages
- 535 Authentication failed — wrong user/pass or unverified sender
- 554 Message rejected — policy, spam content, or missing DNS
- 421 Try again later — rate limit; enable throttling in Senddera
- Connection timed out — firewall, wrong port, or host down
Broader delivery issues: Debugging delivery issues and reading logs.