I do believe there is another issue with this transfer and email services from Yahoo. I am bringing it up on this thread because it does deal with Thunderbird as an email client. And, I think people who use TB use it because they like the control that TB provides.
I noticed I was not receiving some of the emails I usually do. I read another thread that said Yahoo was "hiding" spam emails. I logged into the web based Yahoo to check the spam folder and there they were. Yahoo filtered what messages it thought was spam, never making it the the inbox for Thunderbird to do any filtering. Me being me, I selected everything and marked it as not spam and return them to the inbox, I then let TB do the filtering. If this messes with Yahoo's algorithms, so be it.
Thanks for your input. As a result, I logged in to the Yahoo webmail and also found that the spam folder contained unspam emails. I "turned off" the spam filter by using the approach given in the below link. I would much sooner have all emails come into Thunderbird and let me deal with spam locally.
https://clusterednetworks.com/blog/post/how-turn-spam-filtering-yahoo-email
Since I just did this, it's not yet a tested solution, but I don't see why it won't work.
