Can send email to user via telnet from anywhere. Why?

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nektod
Posts: 2
Joined: Tue Aug 16, 2016 2:06 pm

Can send email to user via telnet from anywhere. Why?

Postby nektod » Tue Jun 30, 2020 11:30 am

Hi!

I've discovered that can send email to real users mailbox from anywhere without auth via telnet:

Code: Select all

open myzimbra.server.com 25
220 myzimbra.server.com ESMTP Postfix
helo myzimbra.server.com
250 myzimbra.server.com
mail from:<user1@server.com>
250 2.1.0 Ok
rcpt to:<user2@server.com>
250 2.1.5 Ok
data
250 2.0.0 Ok: queued as E90CC3E14E3


In zimbra.log:

Code: Select all

Jun 30 11:30:17 mail postfix/cleanup[131061]: 27F193E1B32: message-id=<20200630103011.27F193E1B32@myzimbra.server.com>
Jun 30 11:30:17 mail postfix/qmgr[131037]: 27F193E1B32: from=<user1@server.com>, size=343, nrcpt=2 (queue active)
Jun 30 11:30:17 mail amavis[118405]: (118405-06) ESMTP [127.0.0.1]:10024 /opt/zimbra/data/amavisd/tmp/amavis-20200630T131633-118405-9FRJEEKE: <user1@server.com> -> <user2@server.com> SIZE=343 Received: from  myzimbra.server.com ([127.0.0.1]) by localhost (myzimbra.server.com [127.0.0.1]) (amavisd-new, port 10024) with ESMTP; Tue, 30 Jun 2020 11:30:17
Jun 30 11:30:17 mail amavis[118405]: (118405-06) Checking: BVGVNeh714dP [my.external.ip] <user1@server.com> -> <user2@server.com>
Jun 30 11:30:22 mail postfix/amavisd/smtpd[636]: connect from localhost[127.0.0.1]
Jun 30 11:30:22 mail postfix/amavisd/smtpd[636]: 34A6C3E1B34: client=localhost[127.0.0.1]
Jun 30 11:30:22 mail postfix/cleanup[131053]: 34A6C3E1B34: message-id=<20200630103011.27F193E1B32@myzimbra.server.com>
Jun 30 11:30:22 mail amavis[118405]: (118405-06) BVGVNeh714dP FWD from <user1@server.com> -> <user2@server.com>, BODY=7BIT 250 2.0.0 from MTA(smtp:[127.0.0.1]:10025): 250 2.0.0 Ok: queued as 34A6C3E1B34
Jun 30 11:30:22 mail postfix/amavisd/smtpd[636]: disconnect from localhost[127.0.0.1] ehlo=1 mail=1 rcpt=1 data=1 quit=1 commands=5
Jun 30 11:30:22 mail postfix/qmgr[131037]: 34A6C3E1B34: from=<user1@server.com>, size=938, nrcpt=1 (queue active)
Jun 30 11:30:22 mail postfix/amavisd/smtpd[637]: connect from localhost[127.0.0.1]
Jun 30 11:30:22 mail postfix/amavisd/smtpd[637]: 375A43E1B35: client=localhost[127.0.0.1]
Jun 30 11:30:22 mail postfix/cleanup[131061]: 375A43E1B35: message-id=<20200630103011.27F193E1B32@myzimbra.server.com>
Jun 30 11:30:22 mail postfix/amavisd/smtpd[637]: disconnect from localhost[127.0.0.1] ehlo=1 mail=1 rcpt=1 data=1 quit=1 commands=5
Jun 30 11:30:22 mail postfix/qmgr[131037]: 375A43E1B35: from=<user1@server.com>, size=745, nrcpt=1 (queue active)
Jun 30 11:30:22 mail amavis[118405]: (118405-06) Passed CLEAN {RelayedInbound,RelayedOpenRelay}, [my.external.ip]:63906 [136.243.136.61] <user1@server.com> -> <user2@server.com>, Queue-ID: 27F193E1B32, Message-ID: <2
0200630103011.27F193E1B32@myzimbra.server.com>, mail_id: BVGVNeh714dP, Hits: 2.819, size: 343, queued_as: 34A6C3E1B34/375A43E1B35, 4639 ms
Jun 30 11:30:22 mail postfix/smtp[131055]: 27F193E1B32: to=<user2@server.com>, relay=127.0.0.1[127.0.0.1]:10024, delay=41, delays=36/0/0/4.6, dsn=2.0.0, status=sent (250 2.0.0 from MTA(smtp:[127.0.0.1]:10025): 250 2.0.0 Ok: queued as 34A6C3E
1B34)


So, ZImbra thinks that email's sent from trusted network, localhost. But If I send email to another domain, it'll be blocked as relay access denied. Could you please tell why? :shock:


phoenix
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Joined: Fri Sep 12, 2014 9:56 pm
Location: Liverpool, England

Re: Can send email to user via telnet from anywhere. Why?

Postby phoenix » Tue Jun 30, 2020 11:41 am

nektod wrote:Hi!

I've discovered that can send email to real users mailbox from anywhere without auth via telnet
That's what a mail server is for, it receives mail from anywhere and delivers it to a user. You can't implement authentication on port 25 otherwise you'd never receive mail from people - think about it. :) BTW, using telnet is no different than receiving an email from another server, as long as your server is not an open relay there's no problem with that.
Regards

Bill

Rspamd: A high performance spamassassin replacement

Per ardua ad astra

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