Grav 1.7.38 email via sendmail fails, but direct via sendmail works?

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i use msmtp to send mail on linux

msmtp --version
	msmtp version 1.8.22
	Platform: x86_64-redhat-linux-gnu
	TLS/SSL library: GnuTLS
	Authentication library: GNU SASL; oauthbearer and xoauth2: built-in
	Supported authentication methods:
	plain scram-sha-1 scram-sha-256 external gssapi cram-md5 digest-md5 login ntlm oauthbearer xoauth2
	IDN support: disabled
	NLS: enabled, LOCALEDIR is /usr/share/locale
	Keyring support: Gnome
	System configuration file name: /etc/msmtprc
	User configuration file name: /root/.msmtprc

	Copyright (C) 2022 Martin Lambers and others.
	This is free software.  You may redistribute copies of it under the terms of
	the GNU General Public License <http://www.gnu.org/licenses/gpl.html>.
	There is NO WARRANTY, to the extent permitted by law.

it’s aliased to sendmail

ls -al `which sendmail`
	lrwxrwxrwx 1 root root 21 Jan 21  2021 /usr/sbin/sendmail -> /etc/alternatives/mta*
ls -al /etc/alternatives/mta
	lrwxrwxrwx 1 root root 14 Jan 21  2021 /etc/alternatives/mta -> /usr/bin/msmtp*

msmtprc is configured to send via smarthost

mail send from shell works as expected

echo "hello" | /usr/sbin/sendmail -d -a mainsite myusers@example.com
	loaded system configuration file /etc/msmtprc
	ignoring user configuration file /root/.msmtprc: No such file or directory
	using account mainsite from /etc/msmtprc
	host = smtp.fastmail.com
	port = 465
	source ip = (not set)
	proxy host = (not set)
	proxy port = 0
	socket = (not set)
	timeout = off
	protocol = smtp
	domain = localhost
	auth = choose
	user = myuser@fastmail.com
	password = *
	passwordeval = (not set)
	ntlmdomain = (not set)
	tls = on
	tls_starttls = off
	tls_trust_file = /opt/vmail/myCA.CHAIN.crt.pem
	tls_crl_file = (not set)
	tls_fingerprint = (not set)
	tls_key_file = /opt/vmail/mainsite.key.pem
	tls_cert_file = /opt/vmail/mainsite.crt.pem
	tls_certcheck = off
	tls_min_dh_prime_bits = (not set)
	tls_priorities = (not set)
	tls_host_override = (not set)
	auto_from = off
	maildomain = (not set)
	from = myuser@fastmail.com
	set_from_header = auto
	set_date_header = auto
	remove_bcc_headers = on
	undisclosed_recipients = off
	dsn_notify = (not set)
	dsn_return = (not set)
	logfile = /var/log/msmtp.log
	logfile_time_format = (not set)
	syslog = (not set)
	aliases = (not set)
	reading recipients from the command line
	TLS session parameters:
	    (TLS1.3)-(ECDHE-X25519)-(RSA-PSS-RSAE-SHA256)-(AES-256-GCM)
	TLS certificate information:
	    Subject:
	        C=AU,ST=Victoria,L=Melbourne,O=FastMail Pty Ltd,CN=*.fastmail.com
	    Issuer:
	        C=US,O=DigiCert Inc,CN=DigiCert TLS RSA SHA256 2020 CA1
	    Validity:
	        Activation time: Sun 23 Oct 2022 08:00:00 PM EDT
	        Expiration time: Thu 02 Nov 2023 07:59:59 PM EDT
	    Fingerprints:
	        SHA256: 62:...
	        SHA1 (deprecated): 85:...
	<-- 220 smtp.fastmail.com ESMTP ready
	--> EHLO localhost
	<-- 250-smtp.fastmail.com
	<-- 250-PIPELINING
	<-- 250-SIZE 71000000
	<-- 250-ENHANCEDSTATUSCODES
	<-- 250-8BITMIME
	<-- 250 AUTH PLAIN LOGIN XOAUTH2 OAUTHBEARER
	--> AUTH PLAIN AHB...
	<-- 235 2.0.0 OK
	--> MAIL FROM:<myuser@fastmail.com>
	--> RCPT TO:<myusers@example.com>
	--> DATA
	<-- 250 2.1.0 Ok
	<-- 250 2.1.5 Ok
	<-- 354 End data with <CR><LF>.<CR><LF>
	--> From: myuser@fastmail.com
	--> Date: Fri, 27 Jan 2023 16:50:53 -0500
	--> Message-ID: <362d396899sdfg98s7df9sd8f7h5s9df8f.myuser@fastmail.com>
	--> hello
	--> .
	<-- 250 2.0.0 Ok: queued as EC463513E4F 824BF1248FE via compute2
	--> QUIT
	<-- 221 2.0.0 Bye

the sent mail is received as expected

i run Grav 1.7.38

gpm --version
	Grav Package Manager 1.7.38

email plugin config is via sendmail, using the same sendmail bin string,

cat user/mainsite.net/config/plugins/email.yaml
	enabled: true
	from: myuser@fastmail.com
	from_name: MainSite
	to: myuser@fastmail.com
	to_name: MainSite
	queue:
	  enabled: false
	mailer:
	  engine: sendmail
	  sendmail:
	    bin: '/usr/sbin/sendmail -a mainsite'
	content_type: text/plain
	debug: true
	charset: null
	cc: null
	cc_name: null
	bcc: null
	reply_to: null
	reply_to_name: null
	body: null

attempt to send with Grav cli

bin/plugin email test-email -vvv -t myusers@example.com

fails quietly. no output at console, no logs in

find logs | grep email

and no message sent.

I have no idea how to debug this further.

Any suggestions on how to get this working? Or at least debugged?