Send mail as Multipart only when message contains html body or attachments
Text mail body must be before html mail body
CAPEDWARF-224 Implement processing of bounced emails
Handle GS blob upload.
Upgrade M/R, move appId factories.
Use raw compatibility lookup.
Normalize header lookup.
Do not fwd if over limit.
Use bucket name in blob key.
Abstract storage, use GCS if available.