Tudor Shandrov ยท Technical Noteshttps://notes.shandrov.ru/Practical infrastructure engineering notes.Diagnosing deferred Mailcow delivery: local firewall or remote MX refusal?https://notes.shandrov.ru/notes/mail/mailcow-deferred-remote-mx/https://notes.shandrov.ru/notes/mail/mailcow-deferred-remote-mx/Tue, 15 Sep 2026 00:00:00 GMTA short evidence-driven workflow for distinguishing local SMTP connectivity problems from selective refusal by a remote mail server.Monitoring Proxmox VE with Prometheus using API tokens and a trusted CAhttps://notes.shandrov.ru/notes/monitoring/proxmox-prometheus-api-ca/https://notes.shandrov.ru/notes/monitoring/proxmox-prometheus-api-ca/Tue, 15 Sep 2026 00:00:00 GMTA production-oriented pattern for collecting Proxmox metrics without disabling TLS verification or using a full administrator account.Migrating Ceph authentication keys to aes256k without losing cluster accesshttps://notes.shandrov.ru/notes/storage/ceph-auth-aes256k-migration/https://notes.shandrov.ru/notes/storage/ceph-auth-aes256k-migration/Tue, 15 Sep 2026 00:00:00 GMTA staged operational approach to rotating Ceph service and client keys while preserving quorum and administrative access.