Ensure the SMTP send recorder properly handles the recording of messages
which may have the same body hash but have different recipients. E.g.:
send the same message twice to 2 different users via Bcc.
The send recorder now maintains a list of send requests and waiting for
a message to be sent is done one the oldest of the messages.
Change behavior of `getParentID`: when `getParentID` gets called on an
external ID and more than one message with that ID is found, inspect the
metadata flags and if only one of those messages is `MessageFlagSent`,
then choose that as the parent.
When attaching public key, we take the root mime part, create a new root,
and put the old root alongside an additional public key mime part.
But when moving the root, we would copy all content headers, even empty ones.
So we’d be left with Content-Disposition: "" which would fail to parse.
We now set disposition during attachment upload. However, this presents
a problem: some clients use inline disposition but don't provide a
content ID. Our API doesn't support this. To mitigate the issue, we just
fall back to attachment disposition in this case.
This fixes various race conditions and leaks related to the user's sync
and API event stream. It was possible for a sync/stream to begin after a
user was already closed; this change prevents that by managing the
goroutines related to sync/stream within cancellable groups.
There was a race condition internal to the go-smtp library.
In order to fix it, a version bump was necessary.
However, this significantly changed the library interface.
We need to unlock the user keyring anyway to unlock the address keyring,
so we should just return it instead of re-unlocking the user keyring
when sending a message.
