I think you are good on your mail server for a while.
Linux kernel 6.15 will still boot on a 486. You can pair that with MUSL 1.25 (current) and the latest Busybox to create a perfectly viable Linux system.
Debian Trixie is going to be released in a couple months with kernel 6.12 LTS.
As somebody pointed out in a different post, the Linux Foundation will provide support for kernel 6.12 for 10 years after Debian Trixie is released.
I think you are good on your mail server for a while.
Linux kernel 6.15 will still boot on a 486. You can pair that with MUSL 1.25 (current) and the latest Busybox to create a perfectly viable Linux system.
Debian Trixie is going to be released in a couple months with kernel 6.12 LTS.
As somebody pointed out in a different post, the Linux Foundation will provide support for kernel 6.12 for 10 years after Debian Trixie is released.
https://www.cip-project.org/about/linux-kernel-core-packages
So, there will be a supported kernel that can be compiled for the 486 until mid 2035 at least.