The logic as described above makes total sense (RCPT TO != Header "To:" then use default address). I also want to suggest an option that could be added to the Settings that would reverse the current logic and allow us to prefer Header "To:" to RCPT TO if the To address is in your list of addresses. That would be even more useful for custom domains where the MX isn't proton, as you would then be able to have multiple addresses on your custom domain, that you could then respond to and have it use the correct From address automatically.
Yves
The logic as described above makes total sense (RCPT TO != Header "To:" then use default address). I also want to suggest an option that could be added to the Settings that would reverse the current logic and allow us to prefer Header "To:" to RCPT TO if the To address is in your list of addresses. That would be even more useful for custom domains where the MX isn't proton, as you would then be able to have multiple addresses on your custom domain, that you could then respond to and have it use the correct From address automatically.