"550 5.7.1 Relaying denied" sending via Mailgun with msmtp - email

Question

Has anyone successfully set up msmtp with a Mailgun account? I keep getting "Relaying denied", and msmtp reports that the envelope from is invalid. I have tried every variation of the from address that I can think of, scoured Mailgun's documentation for details on their SMTP parameters, and searched the web for examples, and I've not found anything that differs from my setup (aside from server and account names, of course).
Here is my /etc/msmtprc file,
account default
# The SMTP smarthost
host smtp.mailgun.org
# Use TLS on port 465
port 465
tls on
tls_starttls off
user manul#mail.mydomain.net
password [snip]
from mailgun#mydomain.net
# Syslog logging with facility LOG_MAIL instead of the default LOG_USER
syslog LOG_MAIL
And the msmtp session:
$ echo 'Subject: Grfg' | msmtp -v 'aidalgol#example.net'
loaded system configuration file /etc/msmtprc
ignoring user configuration file /home/me/.msmtprc: No such file or directory
falling back to default account
using account default from /etc/msmtprc
host = smtp.mailgun.org
port = 465
source ip = (not set)
proxy host = (not set)
proxy port = 0
timeout = off
protocol = smtp
domain = localhost
auth = none
user = manul#mail.mydomain.net
password = *
passwordeval = (not set)
ntlmdomain = (not set)
tls = on
tls_starttls = off
tls_trust_file = system
tls_crl_file = (not set)
tls_fingerprint = (not set)
tls_key_file = (not set)
tls_cert_file = (not set)
tls_certcheck = on
tls_min_dh_prime_bits = (not set)
tls_priorities = (not set)
auto_from = off
maildomain = (not set)
from = mailgun#aidalgolland.net
add_missing_from_header = on
add_missing_date_header = on
remove_bcc_headers = on
dsn_notify = (not set)
dsn_return = (not set)
logfile = (not set)
logfile_time_format = (not set)
syslog = LOG_MAIL
aliases = (not set)
reading recipients from the command line
TLS session parameters:
(TLS1.3)-(ECDHE-X25519)-(RSA-PSS-RSAE-SHA256)-(AES-128-GCM)
TLS certificate information:
Owner:
Common Name: *.mailgun.org
Organization: MAILGUN TECHNOLOGIES\, INC
Organizational unit: MAILGUN TECHNOLOGIES\, INC
Locality: San Francisco
State or Province: California
Country: US
Issuer:
Common Name: Thawte TLS RSA CA G1
Organization: DigiCert Inc
Organizational unit: www.digicert.com
Country: US
Validity:
Activation time: Wed 19 Feb 2020 13:00:00 NZDT
Expiration time: Wed 20 Apr 2022 00:00:00 NZST
Fingerprints:
SHA256: 9E:5F:9B:27:BB:26:14:6F:3E:2F:50:75:FE:BF:64:1C:4B:8D:E0:A6:B7:EA:4F:27:13:05:FD:81:3F:57:52:26
SHA1 (deprecated): 54:36:F6:D1:44:0A:B4:62:F0:94:1B:21:7A:1B:82:5C:DF:FD:FF:57
<-- 220 Mailgun Influx ready
--> EHLO localhost
<-- 250-smtp-out-n17.prod.us-east-1.postgun.com
<-- 250-AUTH PLAIN LOGIN
<-- 250-SIZE 52428800
<-- 250-8BITMIME
<-- 250-ENHANCEDSTATUSCODES
<-- 250-SMTPUTF8
<-- 250 PIPELINING
--> MAIL FROM:<mailgun#myexample.net>
--> RCPT TO:<aidalgol#example.net>
--> DATA
<-- 550 5.7.1 Relaying denied
msmtp: envelope from address mailgun#mydomain.net not accepted by the server
msmtp: server message: 550 5.7.1 Relaying denied
msmtp: could not send mail (account default from /etc/msmtprc)

Answer 1

It turned out to be that I needed to set auth on in the msmtp configuration. The error envelope from address mailgun#mydomain.net not accepted by the server from msmtp was completely wrong.

Answer 2

For other people who got here you'll probably need to go to
https://app.mailgun.com/app/sending/domains/**YOUR-DOMAIN-NAME-HERE/credentials
to get your per-domain credentials as suggested here:
https://documentation.mailgun.com/en/latest/quickstart-sending.html#send-via-api
I diagrammed what to put where in the configuration file along with how to navigate to the setting. This should help make things super clear hopefully.
Note: The grey info-box in the bottom right with the password copy thing I got to by clicking on the green outlined "Reset password" button