This article explains how Taguchi's bounce classification system determines when a subscriber email address should be flagged as invalid, the types of bounce codes that contribute to this determination, and the implications for deliverability and subscriber management.

What is an invalid email address?

An invalid email address in Taguchi means that the bounce classification system has determined that a profile with an email address should no longer receive email activities.

Taguchi does not necessarily flag an email address as invalid after a single bounce — it makes multiple delivery attempts and weighs the following factors before making a final determination:

• Number of bounces received
• Type of bounces
• Number of successful deliveries to the address
• Length of time the address has been in the system
• History of interaction from that address (opens, clicks, etc.)

This multi-factor approach ensures that legitimate temporary issues (such as a full inbox or a server outage) do not result in a subscriber being prematurely invalidated.

This process can take up to a week in normal cases (since bounces can come in several days after the message was initially delivered), and as inbox providers update their rules from time to time, we update the rules at our end too.

Why are profiles flagged as invalid?

Invalid flagging is Taguchi's automated deliverability protection — it's designed to prevent you from repeatedly sending to addresses that clearly can't receive mail, which protects your sender reputation. If you have specific addresses you believe have been incorrectly flagged, the best course of action is to raise a support ticket with Taguchi directly.

Identifying an invalid email address

The only reliable way to determine whether an email address is invalid is to send it an email and read the response from the mail server. There is no pre-send validation tool within Taguchi — invalid classification is reactive, based on real delivery feedback received after a send attempt.

To view a bounce reason on a subscriber profile:

1. Navigate to the subscriber profile
2. Locate a bounce event in the interaction history
3. Select the more options button to display the bounce reason and code

You can also generate a 'bounce reasons' extract for a specific cohort of subscribers. This extract provides you with:

• subscriber_id
• bounce_code
• bounce_reason
• last_bounce_timestamp
• invalid_email_timestamp

See: Extracting bounce reasons from Taguchi

Bounce codes & reasons

For a full list of bounce codes that may be returned by receiving mail servers, see Why does an email bounce?

Not all recipient mail servers provide detailed bounce reasons, and in some cases the information returned may be limited. This can make deeper analysis challenging in some instances.

Deliverability

Once an email address is marked invalid, Taguchi will no longer attempt to deliver emails to that subscriber. The address is automatically excluded from all future sends, including API-driven trigger activities.

Distinction from unsubscribed

Invalid and globally unsubscribed are two separate statuses in Taguchi. Active subscribers are defined as those who have neither globally unsubscribed nor been marked as invalid. The key distinction is:

• Invalid — system-driven: determined automatically by the bounce classification system based on delivery failure history
• Globally Unsubscribed — subscriber-driven: the subscriber has opted out of communications

Both statuses result in the address being excluded from sends, but they are recorded and managed separately on the subscriber profile.

Importing invalid email addresses

Taguchi preserves all subscriber preferences and status flags when importing existing subscribers. Invalid status cannot be reset or overridden via a UI import. If an address that has already been flagged as invalid is included in a new import file, the invalid status will be retained — it will not be reinstated as active simply because it appears in a new list.

Spam complaints

When a recipient marks an email as spam using their mail client or inbox provider's reporting function, Taguchi receives a spam complaint notification via a feedback loop. This triggers an automatic response: the subscriber's profile is marked as invalid and globally unsubscribed.

Unlike bounce-based invalid flagging — which uses a multi-factor assessment over time — a spam complaint results in immediate invalidation. This is a legal compliance measure to ensure that any recipient who has explicitly identified your email communication as spam cannot be contacted again under any circumstances.

This behaviour is in place to protect both your sender reputation and your organisation's compliance obligations under applicable anti-spam legislation.

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Related articles

• What is an invalid email address?
• How can I tell if an email address is invalid?
• What are 'Active Subscribers'?
• What is the difference between global unsubscribe vs list unsubscribe?

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If you have questions about invalid email addresses or believe an address has been incorrectly flagged, please open a support ticket and our team will be happy to help.

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