Well apparently Protonmail doesn't support setting the In-Reply-To header manually: https://protonmail.uservoice.com/forums/284483-feedback/suggestions/9655260-make-it-possible-to-use-reply-to-field
However, they're developing an IMAP/SMTP bridge which could be used on Thunderbird which, on the other hand, does have the ability to set the In-Reply-To header, so I wonder if I could do it that way. I'll have to wait for their reply. -- A list of frequently asked questions is available at: http://wiki.panotools.org/Hugin_FAQ --- You received this message because you are subscribed to the Google Groups "hugin and other free panoramic software" group. To unsubscribe from this group and stop receiving emails from it, send an email to hugin-ptx+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/hugin-ptx/BWQAMltkv0cdG3bjpt_iGsS76rbEL8oID7mCrjs_Ba0bcmZut2WcyL0dUktiiw5f43JcLPnPt8MjGwZ05G2BDKo0U8u31JgfIEnNR4eC_4M%3D%40protonmail.com.
