# MAIL FROM and From authorization

Module check.authorize_sender verifies that envelope and header sender addresses belong
to the authenticated user. Address ownership is established via table
that maps each user account to a email address it is allowed to use.
There are some special cases, see `user_to_email` description below.

```
check.authorize_sender {
    prepare_email identity
    user_to_email identity
    check_header yes

    unauth_action reject
    no_match_action reject
    malformed_action reject
    err_action reject

    auth_normalize auto
    from_normalize auto
}
```
```
check {
    authorize_sender { ... }
}
```

## Configuration directives

### user_to_email _table_
Default: `identity`

Table that maps authorization username to the list of sender emails
the user is allowed to use.

In additional to email addresses, the table can contain domain names or
special string "\*" as a value. If the value is a domain - user
will be allowed to use any mailbox within it as a sender address.
If it is "\*" - user will be allowed to use any address.

By default, table.identity is used, meaning that username should
be equal to the sender email.

Before username is looked up via the table, normalization algorithm
defined by auth_normalize is applied to it.

---

### prepare_email _table_
Default: `identity`

Table that is used to translate email addresses before they
are matched against user_to_email values.

Typically used to allow users to use their aliases as sender
addresses - prepare_email in this case should translate
aliases to "canonical" addresses. This is how it is
done in default configuration.

If table does not contain any mapping for the used sender
address, it will be used as is.

---

### check_header _boolean_
Default: `yes`

Whether to verify header sender in addition to envelope.

Either Sender or From field value should match the
authorization identity.

---

### unauth_action _action_
Default: `reject`

What to do if the user is not authenticated at all.

---

### no_match_action _action_
Default: `reject`

What to do if user is not allowed to use the sender address specified.

---

### malformed_action _action_
Default: `reject`

What to do if From or Sender header fields contain malformed values.

---

### err_action _action_
Default: `reject`

What to do if error happens during prepare_email or user_to_email lookup.

---

### auth_normalize _action_
Default: `auto`

Normalization function to apply to authorization username before
further processing.

Available options:

- `auto`                    `precis_casefold_email` for valid emails, `precis_casefold` otherwise.
- `precis_casefold_email`   PRECIS UsernameCaseMapped profile + U-labels form for domain
- `precis_casefold`         PRECIS UsernameCaseMapped profile for the entire string
- `precis_email`            PRECIS UsernameCasePreserved profile + U-labels form for domain
- `precis`                  PRECIS UsernameCasePreserved profile for the entire string
- `casefold`                Convert to lower case
- `noop`                    Nothing

PRECIS profiles are defined by RFC 8265. In short, they make sure
that Unicode strings that look the same will be compared as if they were
the same. CaseMapped profiles also convert strings to lower case.

---

### from_normalize _action_
Default: `auto`

Normalization function to apply to email addresses before
further processing.

Available options are same as for `auth_normalize`.