I can't send mail to another local account using mailutils

[ciscv64]

Since last year, I have a habit : send mail to myself (like write a diary)
In other distro, I simply using mail command and mail will sent successfully to another local account.
But in gentoo, I write and sent but it keep into folder

[alamahant]

You need to install an smtp server first like

[szatox]

Nullmailer only sends emails, it does not receive them.
I'm not sure it's even able to do local delivery, it's supposed to be used with an external mail server.