Replace mhsendmail with msmtp

[lmakarov]

Apparently, there is nothing special in mhsendmail in terms of mail routing to MailHog. mhsendmail is just a MTA that can bridge the gap between PHP and an SMTP server (as PHP cannot natively talk to a SMTP server on Linux).

At the same time, mhsendmail has some bugs and has not been maintained in a while. We should replace it with another MTA.

On Debian, ssmtp used to be a solution for such cases, but it's not maintained anymore.
The option that is more current and maintained is msmtp. More details here.

[lmakarov]

BTW sendmail on Alpine (busybox) can work with SMTP directly (including authentication).

$ docker run --rm alpine sendmail --help
BusyBox v1.28.4 (2018-12-06 15:13:21 UTC) multi-call binary.

Usage: sendmail [-tv] [-f SENDER] [-amLOGIN 4<user_pass.txt | -auUSER -apPASS]
                [-w SECS] [-H 'PROG ARGS' | -S HOST] [RECIPIENT_EMAIL]...

Read email from stdin and send it

Standard options:
        -t              Read additional recipients from message body
        -f SENDER       For use in MAIL FROM:<sender>. Can be empty string
                        Default: -auUSER, or username of current UID
        -o OPTIONS      Various options. -oi implied, others are ignored
        -i              -oi synonym, implied and ignored

Busybox specific options:
        -v              Verbose
        -w SECS         Network timeout
        -H 'PROG ARGS'  Run connection helper. Examples:
                openssl s_client -quiet -tls1 -starttls smtp -connect smtp.gmail.com:25
                openssl s_client -quiet -tls1 -connect smtp.gmail.com:465
                        $SMTP_ANTISPAM_DELAY: seconds to wait after helper connect
        -S HOST[:PORT]  Server (default $SMTPHOST or 127.0.0.1)
        -amLOGIN        Log in using AUTH LOGIN (-amCRAM-MD5 not supported)
        -auUSER         Username for AUTH
        -apPASS         Password for AUTH

If no -a options are given, authentication is not done.
If -amLOGIN is given but no -au/-ap, user/password is read from fd #4.
Other options are silently ignored; -oi is implied.
Use makemime to create emails with attachments.

So in PHP the setting would be:

sendmail_path = '/usr/sbin/sendmail -t -i -S mail:1025'

It's also interesting that busybox can be installed on Debian and replace quite a few system utilities:

$ busybox
...
Currently defined functions:
        [, [[, acpid, adjtimex, ar, arp, arping, ash, awk, basename, blockdev, brctl, bunzip2, bzcat, bzip2, cal, cat, chgrp, chmod, chown, chroot, chvt, clear, cmp, cp, cpio,
        cttyhack, cut, date, dc, dd, deallocvt, depmod, devmem, df, diff, dirname, dmesg, dnsdomainname, dos2unix, du, dumpkmap, dumpleases, echo, egrep, env, expand, expr, false,
        fgrep, find, fold, free, freeramdisk, fstrim, ftpget, ftpput, getopt, getty, grep, groups, gunzip, gzip, halt, head, hexdump, hostid, hostname, httpd, hwclock, id, ifconfig,
        init, insmod, ionice, ip, ipcalc, kill, killall, klogd, last, less, ln, loadfont, loadkmap, logger, login, logname, logread, losetup, ls, lsmod, lzcat, lzma, lzop, lzopcat,
        md5sum, mdev, microcom, mkdir, mkfifo, mknod, mkswap, mktemp, modinfo, modprobe, more, mount, mt, mv, nameif, nc, netstat, nslookup, od, openvt, patch, pidof, ping, ping6,
        pivot_root, poweroff, printf, ps, pwd, rdate, readlink, realpath, reboot, renice, reset, rev, rm, rmdir, rmmod, route, rpm, rpm2cpio, run-parts, sed, seq, setkeycodes, setsid,
        sh, sha1sum, sha256sum, sha512sum, sleep, sort, start-stop-daemon, stat, strings, stty, swapoff, swapon, switch_root, sync, sysctl, syslogd, tac, tail, tar, taskset, tee,
        telnet, test, tftp, time, timeout, top, touch, tr, traceroute, traceroute6, true, tty, udhcpc, udhcpd, umount, uname, uncompress, unexpand, uniq, unix2dos, unlzma, unlzop,
        unxz, unzip, uptime, usleep, uudecode, uuencode, vconfig, vi, watch, watchdog, wc, wget, which, who, whoami, xargs, xz, xzcat, yes, zcat
...

It's very small in size as well:

• busybox - 746 kB installed on disk
• msmtp - 266 kB installed on disk

So, we might as well just use busybox like Alpine.

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Update: busybox on Debian does not implement sendmail. Bummer...