> ## Documentation Index
> Fetch the complete documentation index at: https://docs.mailchannels.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Invalid recipient blocks

> Understand why MailChannels blocks accounts with high invalid-recipient rates and how to resolve an IRR block.

If you receive a bounce with the code `[IRR]`, your account was temporarily blocked because MailChannels detected an unusually high rate of messages addressed to invalid recipients — addresses that don't exist at the receiving mail server.

## Common causes

* **Mailing list hygiene** — the list contains old or mistyped addresses that have never been cleaned.
* **Compromised account** — a spammer has taken over the account and is sending dictionary-attack spam to randomly generated addresses.

## How to resolve an IRR block

<Steps>
  <Step title="Determine the cause">
    Check whether you recently sent to a mailing list, or whether the account may have been compromised. If you did not initiate the sending, treat the account as compromised.
  </Step>

  <Step title="If the account was compromised">
    Change the account password immediately and run a full antivirus and malware scan. Contact your hosting provider if you need help securing the account.
  </Step>

  <Step title="If the block was caused by a mailing list">
    Go through your bounce messages and remove all invalid recipient addresses from the list. Once the invalid-recipient rate returns to normal, the temporary block will lift automatically.
  </Step>
</Steps>

<Note>
  IRR blocks are temporary. The system monitors your invalid-recipient rate and removes the block automatically once the rate drops to acceptable levels. No manual intervention is required once the root cause is addressed.
</Note>