The settings for roadrunner accounts seem to be either secure or not secure:

https://support.mozilla.org/en-US/questions/1311890

If your secure settings have stopped working, it may be because the TWC TLS version is lower than the one required by TB 78. Changing a preference in TB to allow older TLS is probably preferable to using the non-secure settings.

https://support.mozilla.org/en-US/questions/1295861

Or, the TLS is OK, but your antivirus, a common cause of timeouts, is incompatible with the new TB.

The settings for roadrunner accounts seem to be either secure or not secure: https://support.mozilla.org/en-US/questions/1311890 If your secure settings have stopped working, it may be because the TWC TLS version is lower than the one required by TB 78. Changing a preference in TB to allow older TLS is probably preferable to using the non-secure settings. https://support.mozilla.org/en-US/questions/1295861 Or, the TLS is OK, but your antivirus, a common cause of timeouts, is incompatible with the new TB.

No joy.

I've tried secure and insecure, and bumped down the TLS version. I'm getting a time-out to the server or Thunderbird just perpetually attempts to load.

My AV is just Windows Defender; I can't imagine that's the problem.

Just the same, I would add the TB profile folder as an exclusion in WD, in 'Virus and threat protection settings'. Note that some users have to adjust two preferences for TLS.

Adjusted both preferences, turned WD off completely, and still nothing.

stargate525, did you solve your problem?

stargate525, did you solve your problem?

Yes.

Turns out that Spectrum seems to have blacklisted the IP block that ATT uses. Of course no one would actually tell me that.

Switched to a VPN and it works fine.