On Wed, Oct 07, 2020 at 08:02:02PM -0700, li...@lazygranch.com wrote:

> Is there something I should be doing to mitigate this problem?
> 
> Oct  8 02:11:42 myserver postfix/smtpd[11630]: connect from 
> unknown[180.123.163.212]

Were you expecting email from the below network?  If not, you don't
need to worry about bots checking out your MTA.  [ Not all bots are bad,
my DANE survey bot will connect to your MX hosts ~once a day to each MX
host IP address (for those MX hosts that have DANE TLSA records), but it
will politely send "QUIT" after STARTTLS[1] and a post-TLS EHLO. ]

    inetnum:        180.96.0.0 - 180.127.255.255
    netname:        CHINANET-JS
    descr:          Chinanet Jiangsu Province Network
    descr:          China Telecom
    descr:          No.31,jingrong street
    descr:          Beijing 100032
    country:        CN
    admin-c:        CH93-AP
    tech-c:         CJ186-AP
    remarks:        service provider
    status:         ALLOCATED PORTABLE
    remarks:        --------------------------------------------------------
    remarks:        To report network abuse, please contact mnt-irt
    remarks:        For troubleshooting, please contact tech-c and admin-c
    remarks:        Report invalid contact via www.apnic.net/invalidcontact
    remarks:        --------------------------------------------------------
    mnt-by:         APNIC-HM
    mnt-lower:      MAINT-CHINANET-JS
    last-modified:  2016-05-04T00:18:52Z
    source:         APNIC
    mnt-irt:        IRT-CHINANET-CN

    irt:            IRT-CHINANET-CN
    address:        No.31 ,jingrong street,beijing
    address:        100032
    e-mail:         anti-s...@ns.chinanet.cn.net
    abuse-mailbox:  anti-s...@ns.chinanet.cn.net
    admin-c:        CH93-AP
    tech-c:         CH93-AP
    auth:           # Filtered
    mnt-by:         MAINT-CHINANET
    last-modified:  2010-11-15T00:31:55Z
    source:         APNIC

    role:           CHINANET JIANGSU
    address:        260 Zhongyang Road,Nanjing 210037
    country:        CN
    phone:          +86-25-86588231
    phone:          +86-25-86588745
    fax-no:         +86-25-86588104
    e-mail:         jsab...@189.cn
    remarks:        send anti-spam reports to jsab...@189.cn
    remarks:        send abuse reports to jsab...@189.cn
    remarks:        times in GMT+8
    remarks:        www.jsinfo.net
    admin-c:        CH360-AP
    tech-c:         CS306-AP
    tech-c:         CN142-AP
    nic-hdl:        CJ186-AP
    notify:         jsab...@189.cn
    mnt-by:         MAINT-CHINANET-JS
    last-modified:  2020-04-02T09:18:02Z
    source:         APNIC

    person:         Chinanet Hostmaster
    nic-hdl:        CH93-AP
    e-mail:         anti-s...@ns.chinanet.cn.net
    address:        No.31 ,jingrong street,beijing
    address:        100032
    phone:          +86-10-58501724
    fax-no:         +86-10-58501724
    country:        CN
    mnt-by:         MAINT-CHINANET
    last-modified:  2014-02-27T03:37:38Z
    source:         APNIC

-- 
    Viktor.

[1] https://stats.dnssec-tools.org/about.html

If so, you'll see log entries like:

    Oct  7 15:23:51 amnesiac postfix/smtpd[94878]: connect
        from dnssec-stats.ant.isi.edu[128.9.29.254]
    Oct  7 15:23:52 amnesiac postfix/smtpd[94878]:
        Anonymous TLS connection established
        from dnssec-stats.ant.isi.edu[128.9.29.254]:
        TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits)
        key-exchange X25519 server-signature RSA-PSS (2048 bits)
        server-digest SHA256
    Oct  7 15:23:52 amnesiac postfix/smtpd[94878]: disconnect
        from dnssec-stats.ant.isi.edu[128.9.29.254]
        ehlo=2 starttls=1 quit=1 commands=4

    Oct  7 15:23:53 amnesiac postfix/smtpd[94878]: connect
        from dnssec-stats.ant.isi.edu[2001:1878:401::8009:1dfe]
    Oct  7 15:23:54 amnesiac postfix/smtpd[94878]:
        Anonymous TLS connection established
        from dnssec-stats.ant.isi.edu[2001:1878:401::8009:1dfe]:
        TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits)
        key-exchange X25519 server-signature RSA-PSS (2048 bits)
        server-digest SHA256
    Oct  7 15:23:54 amnesiac postfix/smtpd[94878]: disconnect
        from dnssec-stats.ant.isi.edu[2001:1878:401::8009:1dfe]
        ehlo=2 starttls=1 quit=1 commands=4

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