KB5082142 (Windows Server 21H2 CU) + KB5084071 (.NET Framework CU) triggered
cascading Exchange 2016 failures on NEPTUNE today. External SMTP ingest was
restored after 4 fixes (registry ACL on AssistantsQuarantine, Routing Master
DN, disabled messageconcept ExSBR, hosts entries for dead MAIL server). But
internal pipeline (Submission -> categorizer -> mailbox delivery) remained
broken until 3 more fixes (DNS records on ACG-DC16 for n-hosting1/n-largeboxes
/mail, disabled hung DkimSigner agent, disabled IRM to silence RMS Encryption
Agent timeouts). Submission queue still pinned at ~427 messages pre-reboot;
full Neptune reboot queued to clear edgetransport.exe in-memory DNS cache and
pending KB5082142 reboot actions.
All registry/AD/config backups in C:\BackupBeforeFix\ on Neptune. Post-reboot
verification checklist documented in the log.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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