With several accounts connected, the composer treated every account's
identities as "own" when deciding whether a message was self-sent (#703).
A message that account B sent to account A therefore looked self-sent
when replying from A, so the reply was addressed to the original To -
account A itself - and From was switched to B.
Self-sent now means "sent by the account holding the original":
buildReplyRecipients takes an optional selfSentEmails list (defaulting to
ownEmails, so single-account behaviour is unchanged), and the composer
passes the source account's identities there and to the From selection.
Reply-all still drops every connected account's addresses.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>