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Sendgrid uses a large number of IP addresses which may often change. Thus, the small number of IPs may not be sufficient. As Sendgrid is a commercial service with a dedicated support team, they will likely be able to tell you the full list of IPs you need to open or other more appropriate options for your use-case.

Similarly, for NTP, you likely use a pool currently (i.e. SOMETHING.pool.ntp.org) which balances requests via a large and changing list of ntp servers. When using this pool, you likely have to allow outbound UDP 123 to all hosts. If you use a fixed list of NTP server, you need to configure these and thus can restrict packets to these fixed hosts only.

Thank you for your response.
I understand about the IP variation of the Sendgrid and NTP servers.

Please let me check again if there is any possibility of Bitnami communicating towards the Internet with AzureNSG settings on ports 587 and 123.

We would like to check if there is any possibility of unintended communication towards the Internet.

We believe that communications other than the currently configured ports 587 and 123 are blocked by the default deny rules unless explicitly allowed by the NSG outbound rules.

Therefore, if the NSG setting strictly allows only the above IP addresses and ports, then all other Internet communications are basically blocked, correct?

Please let me know. Thank you in advance.

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