Mail

https://mailutils.org/
https://unix.stackexchange.com/questions/695987/how-can-i-make-gnu-mailutils-to-use-an-external-smtp-server

## Internal
echo "[message]" | mail -s "[subject]" [address]
echo "[message]" | mail -E "set verbose" -s "[subject]" [address]

## External SMTP Server
echo "[message]" | mail -E "set sendmail=smtps://[server]" -a "Date: `TZ=Asia/Tokyo date -R`" -a "From: [sender]" -s "[subject]" [address]
echo "[message]" | mail -E "set verbose" -E "set sendmail=smtps://[server]" -a "Date: `TZ=Asia/Tokyo date -R`" -a "From: [sender]" -s "[subject]" [address]

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