Why Use Multiple Sending Servers
A single SMTP server is a single point of failure and a throughput bottleneck. Spreading sends across multiple servers gives you:
- Higher throughput — run parallel delivery queues.
- IP rotation — different recipient ISPs see different source IPs, reducing per-IP reputation risk.
- Failover — if one server goes offline, campaigns continue via the others.
Setting Up a Sending Server Pool
- Add each server under Settings → Sending Servers. Verify SMTP credentials for each.
- Go to Settings → Sending Server Pools → Create Pool.
- Add servers to the pool and assign a weight to each (higher weight = more sends).
| Server | Weight | Role |
|---|---|---|
| smtp-primary | 10 | Main delivery |
| smtp-backup | 5 | Secondary |
| amazon-ses | 3 | Overflow |
Assigning a Pool to a Campaign
When creating a campaign, select the pool under Sending Settings → Sending Server. Senddera will rotate through the pool servers based on weight.
Failover Behavior
Senddera automatically skips a server if it returns a connection error and retries on the next available server in the pool. Mark a server as Inactive manually to remove it from rotation immediately.
Monitoring Per-Server Stats
Check individual server performance under Reports → Sending Servers. Look for:
- Bounce rate per server — indicates IP reputation issues.
- Deferred rate — indicates throttling by receiving ISPs.
- Queue depth — indicates a bottleneck on that server.
Rotate out any server with a bounce rate above 3%.