Why does my Linear issue show Unknown customer when linked from Plain?
Linear shows Unknown customer when the thread's customer has a free or public email address, such as gmail.com or yahoo.com. Linear's API requires every customer to have a unique business domain, so Plain files the request without a customer. The issue is still linked. Only the attribution is missing.
What Plain does
When you link a thread to a Linear issue, Plain finds or creates a Linear Customer from the customer's email domain and files a Customer Request against it. With a business domain such as acme.com, the linked issue shows the customer name.
This behavior started in August 2025. Before then, Plain tried to create a Linear customer with the public domain, Linear rejected it silently, and the customer request was never filed.
Is there a workaround?
No. There is no setting in Plain to override this. Attribution only appears when the customer contacts support from a business email address. If most of your end-users use consumer email, expect Unknown customer on most linked issues.
Business email but still Unknown customer
If the customer has a business domain and the issue still shows Unknown customer:
- Check that the customer's email in Plain is correct and not on a free provider.
- Check whether a company or tenant is associated with the thread. Plain falls back to the company domain if the email domain cannot be matched.
- If the problem persists, share the thread reference with Plain support.