CRL Cheking from .NET App in IIS proxy bypass

Question

I have a commercial .NET app running in IIS (Win2022). The server does not have direct access to internet, only trough a proxy. Proxy is configured at all level

• netsh winhttp
• internet configuration
• http_proxy, https_proxy system variable (and user variables)
• web.config file off .net application

Still, IIS (w3wp.exe process) bypass the proxy when the .NET application is sending an email and validate revocation of the SMTP server certificate. Using netstat -ano|find "SYN" i can see that the process is bypassing the proxy

C:\Users\myuser>netstat -ano|find "SYN"

TCP server-ip:49783 192.229.211.108:80 SYN_SENT 3752 C:\Users\myuser>tasklist |find "3752"

w3wp.exe 3752 Services 0 292,968 K All HTTP are going trough the proxy except for the revocation check of the SMTP server certificate?

Is there any solution APART opening the firewall port 80 directly, which i really want to avoid?