350-001 · Question #77
You are the network administrator of a medium-sized company, and users are complaining that they cannot send emails to some organizations. During your troubleshooting, you notice that your DNS MX…
The correct answer is C. Allow the email server to send traffic only to TCP port 25. E. Use a separate public IP address for your email server only. Restricting outbound SMTP to TCP port 25 and assigning a dedicated public IP to the email server limits spam exposure and isolates the server's sending reputation to prevent future blacklisting.
Question
You are the network administrator of a medium-sized company, and users are complaining that they cannot send emails to some organizations. During your troubleshooting, you notice that your DNS MX record is blacklisted by several public blacklist filters. After clearing these listings for your IP address, and assuming that your email server has the right virus protection in place, what are two possible solutions to prevent this from happening in the future? (Choose two.)
Options
- AChange your Internet provider.
- BChange your public IP address.
- CAllow the email server to send traffic only to TCP port 25.
- DPut your email server in a DMZ.
- EUse a separate public IP address for your email server only.
How the community answered
(28 responses)- A4% (1)
- B7% (2)
- C79% (22)
- D11% (3)
Why each option
Restricting outbound SMTP to TCP port 25 and assigning a dedicated public IP to the email server limits spam exposure and isolates the server's sending reputation to prevent future blacklisting.
Changing ISPs does not address the root cause of why the IP was blacklisted and does not prevent re-infection or re-listing.
Changing the public IP is a temporary workaround; without fixing the underlying spam issue, the new IP will also be blacklisted.
Configuring the email server to send traffic only on TCP port 25 prevents compromised internal hosts or malware from relaying spam through the server on alternate ports, reducing the risk of re-blacklisting.
Placing the email server in a DMZ improves perimeter security but does not directly prevent the server from sending spam or being blacklisted again.
Using a dedicated public IP address for the email server ensures that any blacklisting affects only that IP and does not impact other services, and it gives administrators a clean, identifiable sending reputation to manage.
Concept tested: Email server blacklist prevention using port restriction and IP isolation
Source: https://learn.microsoft.com/en-us/exchange/mail-flow-best-practices/smtp-submission
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