<html><head><meta http-equiv="Content-Type" content="text/html charset=utf-8"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class="">It seems that Mail.app (and I suspect most “desktop class” clients) can display arbitrary headers. This includes the key “Message-Id” and “In-Reply-To”. So as long as an email client supports adding “In-Reply-To” (not to be confused with “Reply-To”) during composition of an new email, one can use it to retroactively participate a mailman-hosted thread. (the value to use can be found in the mailto: address from the web archive. Too bad Mail.app does’t support this. The internet claims Thunderbird can do this:&nbsp;<a href="http://www.pixelbeat.org/docs/thunderbird-threading.html" class="">http://www.pixelbeat.org/docs/thunderbird-threading.html</a><div class=""><br class=""><div><blockquote type="cite" class=""><div class="">On Feb 6, 2017, at 6:01 PM, Erica Sadun &lt;<a href="mailto:erica@ericasadun.com" class="">erica@ericasadun.com</a>&gt; wrote:</div><br class="Apple-interchange-newline"><div class=""><meta http-equiv="Content-Type" content="text/html charset=utf-8" class=""><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><div class="">And then I thought to myself "Maybe if I reply to daniel+test, you won't see this". Resending to your normal addy.</div><div class=""><br class=""></div><br class=""><div class=""><blockquote type="cite" class=""><div class="">On Feb 6, 2017, at 7:00 PM, Erica Sadun &lt;<a href="mailto:erica@ericasadun.com" class="">erica@ericasadun.com</a>&gt; wrote:</div><br class="Apple-interchange-newline"><div class=""><meta http-equiv="Content-Type" content="text/html charset=utf-8" class=""><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><div class="">Replying off-list. Worked fine. Appeared right in-thread.</div><div class=""><br class=""></div><div class="">-- E</div><div class=""><br class=""></div><br class=""><div class=""><blockquote type="cite" class=""><div class="">On Feb 6, 2017, at 6:57 PM, Daniel Duan &lt;<a href="mailto:daniel+test@duan.org" class="">daniel+test@duan.org</a>&gt; wrote:</div><br class="Apple-interchange-newline"><div class=""><meta http-equiv="Content-Type" content="text/html charset=utf-8" class=""><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><div class="">Here’s my attempt to chime in an existing thread from a newly subscribed email address.</div><div class=""><br class=""></div>&gt; This may help<div class="">&gt;&nbsp;</div><div class="">&gt;&nbsp;<a href="http://webapps.stackexchange.com/questions/23197/reply-to-mailman-archived-message" class="">http://webapps.stackexchange.com/questions/23197/reply-to-mailman-archived-message</a></div></div></div></blockquote></div><br class=""></div></div></blockquote></div><br class=""></div></div></blockquote></div><br class=""></div></body></html>