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:

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.