Which of the following files, when using Sendmail or a similar MTA system, will allow a user to redirect all their mail to another address and is configurable by the user themselves?

`/etc/alias` (or `/etc/aliases`) is a system-wide file managed by the administrator for defining mail aliases and redirections for system accounts, not for individual user configuration.

`/etc/mail/forwarders` is not a standard, user-configurable file for mail forwarding in Sendmail; forwarding rules are typically handled by `~/.forward` for users or `/etc/aliases` for system-wide settings.

`~/.alias` is not a standard configuration file for mail forwarding; user-specific mail aliases are typically defined within the `~/.forward` file itself or through specific mail client configurations.

The `~/.forward` file, located in a user's home directory, is a common mechanism supported by Sendmail and similar MTAs that allows an individual user to specify one or more email addresses to which their incoming mail should be automatically redirected. This file is directly editable by the user to manage their own mail forwarding.