We tried a manual about 10 years ago. (I just looked it up to get the link and it was closer to 15, how time flies) No one read it so it basically lapsed into history, along with the user manuals for just about every other software product on the planet. There is a copy, here but it is very very dated https://archive.flossmanuals.net/thunderbird/ Really this forum is a great way to have someone do the searching for you if you can't find what you want. I certainly would not be paying for an online manual that is a copy of the free one I linked to that is almost 15 years out of date. I would be very leery of any "manual" written more than 90 days ago really as version 128, released in recent weeks, rewrites a lot of things and last years version 115 reinvented a whole lot of wheels. Anything prior to that can really only be considered a pointer. Fundamentally email is a relatively complex topic which for most folk "just works" (It is usually not the software than the book of instructions is required for). It is a more than passing understanding of the IMAP and POP mail protocols and forthcoming will be the Microsoft Exchange proprietary protocol and the highly reliant and basically broken technology used to "scan" incoming mail by "security" software that generates most of the support noise. Finding someone in industry that actually understand mail, rather than Microsoft Exchange and Microsoft Outlook is often something of a challenge. Microsoft embarked on a very successful "in education" product placement, including steep discounts, a generation ago. Now we are seeing graduates that only know Microsoft, have never used a non Microsoft product for business office suite use and have little understanding of the the underlying technologies. Mail on the whole is not difficult, because it is about matching connection parameters set by the mail provider with those on your machine and after that it "just works". Until your antivirus kills it, or someone at Thunderbird changes a default that you have no idea is a "thing" (and a manual will not really help there as most folk just accept defaults so they are not really documented.) Primarily, most issues come from outside Thunderbird and through Thunderbird profile per install. which at times looses a profile and it has to be forcibly restated or rebuilt. See these profile documents. https://support.mozilla.org/en-US/kb/dedicated-profile-thunderbird-installation https://support.mozilla.org/en-US/kb/profiles-where-thunderbird-stores-user-data Message threading. https://support.mozilla.org/en-US/kb/message-threading-thunderbird# Note the default is for new folders but due to bugs repair was loosing per folder settings like threading. Inability to receive message generally comes here https://support.mozilla.org/en-US/kb/cannot-receive-messages

Well, that was an education, and thank you! So I'll have to learn to use the knowledge base. I really appreciate the time you devoted to that explanation. Maybe I can learn enough to be a help to someone else someday. One thing's for sure: I'm going to have to expand my vocabulary. Thunderbird forever!