Bulwark currently sends Email/set create without a messageId property,
leaving Message-ID generation to the JMAP server. Servers typically fall
back to their OS hostname for this (Stalwart, via mail-builder's
`gethostname()`), which produces IDs like:
```
<175234...abc@ip-10-0-12-97.ec2.internal>
```
This is bad for every deployment, in three escalating ways:
1. Information disclosure: the Message-ID travels in every outgoing
message and permanently into archives, quoting, and In-Reply-To /
References of replies. An internal hostname (container name, private
DNS, k8s pod name) is infrastructure detail no recipient should see.
2. Deliverability: spam filters score Message-IDs whose domain part is
not a plausible FQDN or is unrelated to the sender (SpamAssassin
MSGID_FROM_MTA_HEADER and friends). Internal names like
*.ec2.internal or bare container ids read as botnet-ish.
3. Correctness of intent: RFC 5322 §3.6.4 recommends the originator
generate the Message-ID, using a domain it controls, so the id is
meaningful and plausibly unique under that domain's authority. The
sender's own domain is exactly that; the mail server's transient
runtime hostname is exactly not.
Generate the id in `sendEmail()` as `<epoch36>.<uuid>@<sender-domain>`,
taken from the From address (falling back to the login username). The
timestamp prefix keeps ids roughly sortable and adds entropy across
UUID reuse concerns; crypto.randomUUID() is available in every runtime
Bulwark supports (browsers and Node 19+). Per RFC 8621 §4.1.2.3 the
JMAP messageId property carries bare msg-ids (no angle brackets), so
none are added.
Clients that never set messageId also can't thread their own sent mail
reliably until the server echoes the message back; setting it at create
time makes the id known and stable from the start.
No behavior change for servers that honored client-provided ids all
along; servers that previously synthesized an id now simply don't need
to.
