You may come across this Salesforce validation (or deployment) error in a scenario where in your source environment you've made a reference (or references) to username(s) that don't exist in the target environment.

The returned error would be:
​Cannot find a user that matches any of the following usernames: <xxx>; remove the user from the component being deployed or create a matching user in the destination organization. - where <xxx> usually refers to a user's email address.

Based on our observations, these are the metadata types that could throw this error: WorkflowOutboundMessage, ApprovalProcess, Dashboard, ReportFolder or CustomSite.

Based on the message returned by Salesforce, they're suggesting you to remove the username <xxx> from your deployment package, and then to try to re-deploy again to the target environment.
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Alternatively, you can create that user (with the correct username) in your target org first, and then re-attempt the deployment of your original package.

But if the user already exists in the target org (so there's no need to create it), make sure that the username (referenced in the error) assigned to the user in the target org matches the username from the source org - this way your deployment shouldn't fail.
​

If you'd like to try to remove the user from your deployment package, you can download the entire deployment package, then make the change on your local device (within the XML file of affected metadata), and once this step is done you'd use the amended package as a source of a new deployment.
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For detailed guidance on that process, check below article:
​​How can I change the deployment package before deploying?

Use Gearset's environment variables feature to deal with the failing username(s) to either:
- Replace them with a blank,
- Or replace them with a username that's already used in the target org.
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For more guidance on how to resolve this error, check these resources:
​Trailblazer Community (Feb 2022)
​Trailblazer Community (July 2015)
​Sfdx-Hardis Documentation