It has been more than 15 years since the OB25 countermeasures started at the provider, but about two years ago, the mail server of the SMTP-AUTH compatible SUBMISSION port prepared with the OB25 countermeasures at the provider I am using "SMTP-AUTH A new measure has been silently introduced that says "If you specify a mail address other than the authenticated provider's mail address in MAIL FROM :, mail relay will be rejected."
There is no problem if you use it normally (?), But if you get your own domain and operate a mail server (qmail) using dynamic dns, you can send mail from inside with your own domain name. It will be gone.
Recently, I've been playing with qmail and I haven't seen this kind of information, so I think it's a niche. I would like to share the changes in qmail-remote.c to use "address".
You are operating a qmail server with your own domain and the following patches are applied
As shown below, smtproutes is used to request mail delivery to the mail server of the provider, and smtp-auth is performed with the mail address as a client.
touch /var/qmail/control/smtproutes
chown qmailr.root /var/qmail/control/smtproutes
chmod 640 /var/qmail/control/smtproutes
cat > /var/qmail/control/smtproutes << EOF
:Provider mail server FQDN:587 Provider Email Address Provider Email Password
EOF
#Create SMTP AUTH string
printf "%s\0%s\0%s"Provider Email Address Provider Email Address Email Password| openssl base64 -e | tr -d '\n'; echo
#The following base64ized SMTP AUTH character string will be displayed, so copy the displayed characters.
Zm9vQGV4YW1wbGUuY29tAGZvb0BleGFtcGxlLmNvbQBwYXNzd29yZA==
#Connection method when encryption is required
openssl s_client -quiet -ign_eof -connect provider mail server:port number-tls1_2
#Connection method when plain text is acceptable
telnet provider mail server port number
__ When you can connect, the following display will be displayed, so enter only the gray part (the display content will differ slightly depending on the server) __
IP address of Trying mail server ...
Connected to mail server name
Escape character is '^]'.
220 Mail server name ESMTP Service ready
EHLO localhost
250-mail server name
250-DSN
250-8BITMIME
250-PIPELINING
250-AUTH=LOGIN
250-AUTH LOGIN CRAM-MD5 PLAIN
250 SIZE 20971520
ʻAUTH PLAIN Pre-created SMTP AUTH string 235 PLAIN authentication successful MAIL FROM: [email protected]***… Acceptance is rejected if MAIL FROM is different from the SMTP-AUTH address *** 553 MAIL FROM:<[email protected]> does not match authenticated user name MAIL FROM: Provider's email account***… Accepted if MAIL FROM is the same as the SMTP AUTH username *** 250 MAIL FROM: <provider email account> OKQUIT`
If it is not accepted, change the area around line 264 of qmail-remote.c so that the SMTP-AUTH email address is specified in MAIL FROM :. (Commented out is the code before the change)
qmail-remote.c
substdio_put(&smtpto,auth_smtp_user,auth_smtp_user.len); // substdio_put(&smtpto,sender.s,sender.len);
After that, as usual (please stop qmail if necessary)
make setup check