> By default Thunderbird tries to send all my outgoing mail through 1 smtp account.
This is the sane default. Your average access provider gives you an smtp server. Your average mail provider, if it provides smtp, may give you an smtp server that will rewrite your enveloppe and worse that is not available everywhere. So the smtp server to use should depend on where your computer is, not which mail account you are using.
> Not doing so can mark your "from" field incorrectly (has happened to me many times) trigger red flags (happened to me before) and make other email clients mark your email as "Gmail thinks this message is a scam".
See it is better to have only one good smtp server to configure to avoid those problems.
Among the 10 email addresses I have, only 6 are linked to an smtp server and exactly one implements spf.
This makes me think that today, defaulting to using one smtp for all accounts is saner than bugging the user and having 8 out of 10 mail accounts that cannot send mails.
This is the sane default. Your average access provider gives you an smtp server. Your average mail provider, if it provides smtp, may give you an smtp server that will rewrite your enveloppe and worse that is not available everywhere. So the smtp server to use should depend on where your computer is, not which mail account you are using.
> Not doing so can mark your "from" field incorrectly (has happened to me many times) trigger red flags (happened to me before) and make other email clients mark your email as "Gmail thinks this message is a scam".
See it is better to have only one good smtp server to configure to avoid those problems.