How Do I Troubleshoot Email Bounces and Suppression in Piano ESP?

Key Concepts

Bounce Types

Soft Bounce (Temporary Failure)

Common causes:

Recipient mailbox is full or temporarily inactive.
Recipient mail server is temporarily down, unreachable, or rate-limiting.
Temporary policy or filtering decisions (sometimes content-related).

Behavior: The provider may retry delivery for a period (commonly up to approximately 72 hours). If the temporary issue persists, the event may eventually become a permanent failure.

Hard Bounce (Permanent Failure)

Common causes:

Invalid recipient address or mailbox does not exist.
Non-existent domain.
Permanent rejection (including strict policy, authentication failures, or blocks).

Behavior: The message is not retried. The address is typically suppressed to protect sender reputation and prevent future delivery attempts.

Deferrals (Temporary Delays)

A deferral is not an immediate failure. It means the receiving server is asking the sender to try again later, often due to volume limits, temporary throttling, or transient server conditions. Delivery may succeed later. If it does not, it can eventually result in a hard bounce.

Resending while a message is deferred can lead to duplicate deliveries if the original message later succeeds.

Subscriber Status Codes in Piano ESP

Subscriber status in Piano ESP determines whether a contact will receive emails. Use these codes to diagnose delivery issues:

Status Code	Meaning	Impact on Delivery
`1`	Subscribed (Active)	Will receive emails.
`0`	Not subscribed (deactivated via API, dashboard, or email)	Will not receive emails.
`-2`	Hard bounce (invalid email / bad email)	Prevented from future sends until cleared/reset.
`-3`	Marked as spam	Prevented from future sends.
`-9`	Blacklisted by ESP	Prevented from future sends.

The ESP UI typically does not provide a complete recipient-level report for soft bounces or deferrals. Hard bounces (-2) and spam/blacklist statuses (-3, -9) are the most actionable statuses for troubleshooting.

How to Check a Subscriber's Bounce Status

To check the status of individual subscribers in a mailing list:

Navigate to Emails → Mailing lists.
Open the three-dot menu (⋮) for the relevant mailing list.
Select Download mailing list.
Open the downloaded CSV and review the status column (commonly column B).

Use the status codes in the above section to interpret the values.

Troubleshooting ESP Delivery Issues

Check the Subscriber's Status

If a subscriber is not receiving newsletters, the first step is to download the mailing list CSV and check their status:

If the status is -2 (hard bounce), the address has been marked as invalid and is suppressed from future sends.
If the status is -3 (spam) or -9 (blacklisted), the subscriber has been suppressed due to a complaint or risk signal.
If the status is 0, the subscriber has been deactivated and will not receive emails until resubscribed.

Clear a Hard Bounce or Suppression Status

If you have confirmed that the email address is valid and should receive emails again (e.g., a mailbox was temporarily deprovisioned and later restored):

Correct the underlying cause (typo, invalid domain, mailbox state).
Request that the hard bounce or suppression status be cleared/reset via Piano Support.
Ensure the subscriber is resubscribed (status 1) to the relevant mailing list(s).

If the address is truly invalid, it will bounce again after being re-enabled. Only clear bounce statuses when you have confirmed the address is valid.

Address Soft Bounces and Deferrals

Soft bounces and deferrals are usually recipient-side issues and often resolve within approximately 72 hours.

Recommended actions:

Ask the recipient to check their spam/junk folder and mark the message as Not Spam.
Ask the recipient (or their IT team) to allowlist your sending domain and address. In some corporate environments, allowlisting sending IPs may also be necessary.
Avoid resending immediately — this can create duplicate deliveries and harm sender reputation.

Content and Security-Gateway Rejections

Some corporate email gateways reject messages containing certain elements (e.g., tracking links) or flagged content. If you see content-related rejections:

Simplify the email content (remove problematic links or elements).
Test sending again after making changes.

Investigate Deliverability Spikes

If you see sudden increases in soft bounces or deferrals across multiple domains (e.g., iCloud, Hotmail, T-Online):

Check whether your sending IPs or domains are on common blacklists.
Review email authentication: SPF, DKIM, and DMARC.
Perform mailing list hygiene: remove inactive users, validate addresses, and avoid purchased or scraped lists.

Some ESP configurations may use different IP pools (e.g., quarantine vs. main pool) based on risk signals such as spam trap hits. Improving list quality is the primary way to restore normal deliverability over time.

Resending to Bounced Recipients

Piano ESP may not automatically resend to soft-bounced recipients. If you need to reattempt delivery to affected users, create a new campaign targeting those subscribers specifically.

Before resending, ensure the subscriber's status has been corrected (if it was a hard bounce) and that the underlying delivery issue has been resolved. Resending to addresses that are still bouncing will further harm your sender reputation.

When to Contact Piano Support

Contact Piano Support when you need:

Assistance clearing hard bounce, spam, or blacklist statuses when self-service is not available.
Investigation of widespread deliverability issues (domain blocks, IP reputation problems, authentication misconfiguration).
Help confirming backend bounce reasons not shown in the ESP UI.

When escalating, include:

Campaign identifier and approximate send time
Recipient address(es) affected
Status codes from the mailing list CSV download
Any bounce or error text the recipient's IT team can provide (full email headers are especially useful)

Last updated: June 26, 2026