Thunderbird always uses the sender address (From) as the return-path ("MAIL FROM:" in SMTP protocol) With recent new legal requirements (at least in France), this MUST be validated by the SMTP server Ex: smtp.orange.fr only accepts mail from *@orange.fr mail.gandi.net, when user is foo@domain.tld, only accepts mail from foo@domain.tld This makes it impossible to use aliases for a personal domain Proposal: allow to use SMTP user login in mail envelope (in "MAIL FROM:" for SMTP protocol, so as return-path) instead of profile email (sender) I have written a small patch: https://rpms.remirepo.net/temp/remi.patch Of course, this is only a prof of concept, unsuitable for everyone, and requires some config option for the SMTP server. I'm building Thunderbird with this patch and I've been using it for weeks, it works. Sent email has return-path set to my ISP address, and "From:" to my alias. I think this conforms to the mail protocol.
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