Simulate regular mail binary on macOS using Mail.app because I don't have the patience to configure postfix once a blue moon.

mail-app

#!/bin/bash

# Original code Copyright (c) 2024 Shane Celis[1]
# Licensed under the MIT License[2]
#
# [1]: https://mastodon.gamedev.place/@shanecelis
# [2]: https://opensource.org/licenses/MIT

# mail-app
#
# Simulate regular mail binary but using Mail.app instead because configuring
# postfix is something I don't have the patience for.

script_name="$(basename $0)";

function usage() {
    echo "usage: $script_name [-hn] [-s subject] [-f from-addr] to-addr ..." >&2;
    echo "       -h help, show usage (this)" >&2;
    echo "       -f the from address, must be an account of Mail.app" >&2;
    echo "          addr format: 'name@email.com' or 'First Last <name@email.com>'" >&2;
    echo "       -n dry run, do not send message, opens in Mail.app" >&2;
    echo "Simulates Unix 'mail' binary using Mail.app" >&2;
    exit 2;
}

from="";
subject="";
dryrun=0;
while getopts hnf:s: opt; do
    case $opt in
        h) usage;;
        n) dryrun=1;;
        f) from="sender: \"$OPTARG\",";;
        s) subject="$OPTARG";;
        *) echo "error: invalid option given." >&2; usage;;
    esac
done
shift $[ OPTIND - 1 ]

if [ $# -lt 1 ]; then
    echo "error: must provide at least one email address." >&2;
    usage;
fi

# Join addresses into a comma-separated string.
addresses=$(printf '"%s", ' "$@")
# Remove last comma.
addresses=${addresses%, }

if [ -z "$subject" ]; then
    echo -n "Subject: ";
    read subject;
fi

# Read from stdin.
body="$(cat)";

osascript <<EOF
set addresses to {$addresses}
set dryrun to $dryrun
tell application "Mail"
    set msg to make new outgoing message with properties {$from subject:"$subject", content:"$body"}
    tell msg
        repeat with addr in addresses
            make new recipient at end of to recipients with properties {address: addr}
        end repeat
    end tell
    if dryrun is 0 then
        send msg
    end if
end tell
EOF