Thanks Zach,
Port 25 is open for Any source and destination in the firewall. And IP address also checked for port 25.
I found this in the logs so I think this means the problem is probably with the Azure IP configuration:
[2022.10.12] 05:10:01.812 [55057213] Initiating connection to 74.125.137.27
[2022.10.12] 05:10:01.812 [55057213] Connecting to 74.125.137.27:25 (Id: 1)
[2022.10.12] 05:10:01.812 [55057213] Binding to local IP 10.0.2.5 (Id: 1)
[2022.10.12] 05:10:01.812 [55057213] Exception connecting to 74.125.137.27 (Id: 1)
[2022.10.12] 05:10:01.812 [55057213] System.Exception: Exception: Connection failed
[2022.10.12] at MailService.RelayServer.Clients.SMTP.ClientConnectionSync.Connect(Int32 connectionId, Int32 timeout)05:10:01.812 [55057213] Previous connection attempt failed. Attempting again with primary local ip.
[2022.10.12] 05:10:01.812 [55057213] Connecting to 74.125.137.27:25 (Id: 2)
[2022.10.12] 05:10:01.828 [55057213] Connection to 74.125.137.27:25 from 10.0.2.4:52044 succeeded (Id: 2)
[2022.10.12] 05:10:02.062 [55057213] RSP: 220 mx.google.com ESMTP n8-20020a63b448000000b0045c88c3b799si17066466pgu.709 - gsmtp
Now I see that the new NIC says "No network access" and it is missing a default gateway.
I will poke around the Azure settings and reboot the server later tonight.
Thanks for the suggestions.