Postfix: SMTP Options with Webmin
| Postfix: SMTP Options with Webmin |
| Server - Postfix |
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There are a number of options available for the SMTP settings.
Each of the options has a link with additional information that is helpful. However, some detail on several of these options is required.
Helo is required When communicating with other mail servers you may request all clients to issue a HELO or a EHLO statement when they connect to your server (RFC 821, RFC 2821). These are rules that everyone should play by but Postfix does not enforce them by default as you can see in the next example no HELO or EHLO was issued.
postconf -d smtpd_helo_restrictions smtpd_helo_restrictions =
telnet testub.example.com 25 Trying 127.0.0.1... Connected to testub.example.com. Escape character is '^]'. 220 testub.example.com ESMTP Postfix (Ubuntu) MAIL FROM:<test.example.com> 250 Ok RCPT TO:< This e-mail address is being protected from spambots. You need JavaScript enabled to view it > 250 Ok DATA 354 End data with <CR><LF>.<CR><LF> test message with no HELO . 250 Ok: queued as 9CE39794BF8 QUIT 221 Bye
Now if you add smptd_helo_required to the main.cf file you will see it has an immediate impact.
smtpd_helo_required = yes
Be sure to reload Postfix. Now view the results.
telnet testub.example.com 25 Trying 127.0.0.1... Connected to testub.example.com. Escape character is '^]'. 220 testub.example.com ESMTP Postfix (Ubuntu) MAIL FROM:<test.example.com> 503 Error: send HELO/EHLO first
Note: The only way that you will be able to do any helo checks is if you require the helo, so this is an important setting to turn on. Allow untrusted routing
Restrict ETRN commands This is a special setting that prevents clients that may request that the mail queue be flushed. This is a setting used for organizations that have intermittent connections. With the ETRN an organization can tell Postfix to deliver all mail at one time. By default there are no restrictions.
postconf -d smtpd_etrn_restrictions smtpd_etrn_restrictions =
With this setting only the mynetworks will be able to issue this command.
smtpd_etrn_restrictions = permit_mynetworks, reject
Here is an example:
Some of the options are covered in other sections of Webmin.
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