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Sophos UTM 9.719-3 - Home User
Virtual machine on Dell Optiplex 3070
i3-9100 @ 3.60 GHz, 16 GB RAM
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Your server starts an SMTP conversation with HELO sophos.mysite.com, the receiving server does an rDNS lookup and then compares the results to the hostname you announced with your HELO command.
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Sophos UTM 9.719-3 - Home User
Virtual machine on Dell Optiplex 3070
i3-9100 @ 3.60 GHz, 16 GB RAM
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The only critical thing here is that there's a valid rDNS PTR record containing sophos.mysite.com.
The MX records for the domains can continue to use mysite.com although sophos.mysite.com would be best practice.
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Sophos UTM 9.719-3 - Home User
Virtual machine on Dell Optiplex 3070
i3-9100 @ 3.60 GHz, 16 GB RAM
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Owner: Emmanuel Technology Consulting
Former Sophos SG(Astaro) advocate/researcher/Silver Partner
PfSense w/Suricata, ntopng,
Other addons to follow