From Newsgroup: alt.privacy

A PAC (Proxy Auto Config) file is a JavaScript file used by browsers or
other applications that support the PAC standard. For each URL or host it decides whether to send the request through a proxy or connect directly. It only works for software that can load and follow a PAC file. PAC files are generally limited to controlling HTTP and HTTPS traffic and do not handle other protocols such as IMAP or SMTP. Programs that ignore proxy settings
such as Thunderbird or Betterbird (which are not browsers) will not be affected.

To make Thunderbird follow proxy rules we need an external tool that can intercept its connections. My first choice would be an open source
proxifier such as SocksCap64 which can force Thunderbird to use a proxy. However SocksCap64 cannot apply different rules for different domains and
will send all traffic through the same proxy without selective routing.
<https://sourceforge.net/projects/sockscap64/>

<https://netactuate.dl.sourceforge.net/project/sockscap64/SocksCap64-setup-3.6.exe>
Name: SocksCap64-setup-3.6.exe
Size: 6193115 bytes (6047 KiB)
SHA256: B2DA49EC9A2702CFD7625D3F152AF98A4C8E3E155DAB78686962BB3DF1F76825

This is where the cross-platform open-source NekoBox may come in handy.
<https://github.com/MatsuriDayo/nekoray

<https://github.com/MatsuriDayo/nekoray/releases/download/4.0.1/nekoray-4.0.1-2024-12-12-windows64.zip>
Name: nekoray-4.0.1-2024-12-12-windows64.zip>
Size: 41719145 bytes (39 MiB)
SHA256: A492224792C38BD1A3B7A5438B1431C5CB4260F55E9A121DB3B2CE1603F7664A

NekoRay or NekoBox is an open source V2Ray/Sing box proxy manager with a graphical interface that sits between our applications & our upstream
proxy such as Psiphon. Unlike proxifiers such as SocksCap64, NekoBox can
apply user-defined specific-domain routing rules so that some domains or IP ranges go through a proxy while others connect directly (bypassing
proxies).

NekoRay can also handle multiple protocols including HTTP HTTPS SOCKS
IMAP SMTP and more which allows it to apply selective routing to non HTTP traffic. By pointing Thunderbird to NekoBox instead of directly to Psiphon
we should be able to recreate the selective routing logic of a PAC file and apply it to applications that do not support PAC files at all.

In practice this means we can keep using the PAC file to control proxy behavior for web browsers exactly as we do now while letting NekoRay handle the same selective routing for Thunderbird. We would configure NekoRay so
that Gmail IMAP and SMTP servers are marked as direct connections and all other destinations are sent through Psiphon. Thunderbird would be pointed
to NekoRay's local listener instead of Psiphon directly so NekoRay can
enforce those rules. The end result is a unified setup where browsers
follow the PAC file and non browser applications such as Thunderbird follow equivalent rules inside NekoRay giving us consistent split tunnel behavior across all software.

I am testing it as we speak but I post this 1st to ask if anyone has a
better solution to force Thunderbird to selectively route so that all
traffic goes through the proxy except the Google GMail server traffic.
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