Somewhat tired of Thunderbird continually mysteriously hanging on me I downloaded and installed the current nightly trunk build. So far, not as much hanging, plus a new update every day, seemingly fixing some bugs (certainly crashing ones I experienced and reported). However it did seem to handle some account settings differently as it complained that my mail server didn’t support SMTP-AUTH, whereas it’d never complained about this previously. I managed to fix this by opening the ‘Account Settings’ panel, scrolling to the end where the Outgoing SMTP accounts are listed after all the accounts for receiving mail, and then unchecking the “Use username and password” option for the appropriate accounts.