Thunderbird somehow after torbirdy removed because of its outdated and not compatible with the current Thunderbird version, trying to link your email smtp/pop over tor hidden services just doesnt work. I tried this with riseup and danwin1210 email providers both doesnt work, Testing it using plain debian + tor + proxychains + thunderbird it will work fine.
I opened ticket with riseup they confirmed to me that all their servers working and they are using onion hidden services.
if you’re using qubes, that may be the difference. This is with kvm on a debian host. there’s nothing particularly modified about it. whonix firewall is at deafults. thunderbird connection ip/port = 10.152.152.10:9102
the same thing will happen on debian for apt. this is assuming a non-whonix like install. in such a scenario, if tor is not running, the software will not try to connect to an onion for privacy purposes, since your isp could see that you made a request to a specific “onion.” in short, it’s to keep site specific leaks from happening that could correlate a user to a site.
Firefox and Thunderbird are developed from perspective of clearnet
users. I.e. users who don’t use Tor.
Such users when entering an onion domain would not be able to reach them
because they don’t use Tor. But the browser / e-mail client’s DNS lookup
for the onion would be visible by the usual DNS server of the user -
which is in most cases the user’s ISP.