I am experiencing a problem using Thunderbird 91.10.0 when attempting to log-in to my ISP's POP3 mail server. The problem does not occur all of the time, however, once it occurs it persists for days. The ISP's POP3 mail server uses SSL/TLS with Normal Password Authentication on port 995. I never permit Thunderbird to "rememeber " the password for this account. The issue is that after entering a valid password in the "Enter your Password" pop-up dialog box and subsequently receiving no error messages, no e-mails are fetched. When using a web browser interface to the same POP3 server it can be seen that quite a few e-mails are present. As an interesting tidibt, it was discovered that entering an incorrect/invalid password in the "Enter your Password" pop-up dilog box produces the same incorrect result. For this interaction I would have expected the "Sending of username did not succeed. Mail server responded: authentication failed: LOGIN failed" pop-up. However, this does not occur. So, my ISP and I would like to know if there is some facility within Thunderbird to trace the request and response interactions between Thunderbird and the POP3 server. If so, how do I enable it and see the corresponding information? At this point we (me and the ISP) do not understand what's going on leading to the incorrect and unexpected behavior. As another tidbit of information, things work correctly when running Thunderbird 60.5.1 interacting with the same ISP. Even a very old version (45.7.0) of Thunderbird works fine with the same ISP (all connections settings are the same). This is all very strange!