I believe Gmail will thread when the message I'd and/or references reference each other. (Otherwise it's hit or miss, like you said.) https://cr.yp.to/immhf/th

I believe Gmail will thread when the message I'd and/or references reference each other. (Otherwise it's hit or miss, like you said.) https://cr.yp.to/immhf/thread.html https://cr.yp.to/immhf/thread.html