Sender Reputation

Bounce Rate Impact & Sender Health Calculator

Evaluate hard and soft bounce percentages against mailbox provider suppression thresholds.

Total Messages Attempted 100,000

Hard Bounces (550 User Unknown) 1,500 (1.5%)

Soft Bounces (421/450 Throttled / Full) 2,200 (2.2%)

Hard Bounce Rate

1.50%

Safe (< 2.0% Threshold)

Soft Bounce Rate

2.20%

Transient ISP deferrals

Total Bounce Rate

3.70%

Combined bounce velocity

Reputation Health Status

HEALTHY

Low risk of ISP suspension

Automated Diagnostic & Mitigation

Your hard bounce rate is currently within acceptable tolerances (<2%). Continue real-time email verification on all lead capture endpoints to prevent aged address pollution.

Automate Real-Time Bounce Suppression

AutoSMTP integrates real-time FBL and SMTP return-path processing to protect IPs automatically.

Deploy Dedicated MTA →

The Difference Between Hard Bounces and Soft Bounces

Mailbox providers treat bounce codes as direct indicators of list hygiene and sender intent. Understanding the root causes of SMTP return codes is critical for maintaining high delivery velocity.

Hard Bounces (5xx Permanent)

Code 550 5.1.1 User unknown indicates the mailbox does not exist. Sending repeatedly to dead addresses triggers automated spam traps and permanent IP blocks.

Soft Bounces (4xx Transient)

Code 421 4.7.0 Rate limit exceeded or 452 Mailbox full. These represent temporary issues. MTAs should back off and retry with exponential delays.

Instant Hard Suppression

Any recipient address that returns a 5xx fatal bounce must be automatically added to your suppression list to prevent future delivery attempts.