Messaging
Threads, quotas, archive, block, report, retention.
Private messages link two accounts. One thread per pair.
Limits
Body: 2000 characters.
Sends are rate-limited.
Actions
Archive / unarchive, block (no more messages), report. A messaging sanction stops writing.
Retention
730 days after the thread’s last message. An active thread does not lose its first messages.
The “new message” email can be turned off in Notifications.