Configuring Multiple Sending Servers

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#

1. Add each server under Settings → Sending Servers. Verify SMTP credentials for each.
2. Go to Settings → Sending Server Pools → Create Pool.
3. Add servers to the pool and assign a weight to each (higher weight = more sends).

Assigning a Pool to a Campaign#

When creating a campaign, select the pool under Sending Settings → Sending Server. AcelleMail will rotate through the pool servers based on weight.

Failover Behavior#

AcelleMail 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%.