# `Mutare.Swoosh.Header`
[🔗](https://github.com/foxbenjaminfox/mutare_swoosh/blob/v0.2.1/lib/mutare/swoosh/header.ex#L1)

:swoosh_header removes custom email headers.

A `Swoosh.Email.header(email, name, value)` call collapses to the email (a piped stage to
what was piped into it). In Swoosh.Email.new/1, a `headers:` option with a literal map (or keyword) value has
one entry dropped per mutant; for an opaque value (a variable, a call), the whole `headers:`
option is dropped instead. An empty literal `headers:` value produces no mutations — removing
nothing is a no-op.

A survivor means no test asserts the header — precisely the tracking, list-management, and
provider-routing headers that are set and never checked.

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*Consult [api-reference.md](api-reference.md) for complete listing*