Install this package:
emerge -a mail-mta/esmtp
If the package is masked, you can unmask it using the autounmask tool or standard emerge options:
autounmask
emerge
autounmask mail-mta/esmtp
Or alternatively:
emerge --autounmask-write -a mail-mta/esmtp
<pkgmetadata> <upstream> <remote-id type="sourceforge">esmtp</remote-id> </upstream> </pkgmetadata>