Editing Training 2022 Linux team/ (section)

==Training on Mail Sending & Receving Problem & Bouncing Problem Part-2 . Dated 02 Feb 2022 - Tetra Support Staff - Biswajit Banerjee==

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'''Video summary:''' "Training Sending,Recieveing Bouncing part2" -- continues directly from Part 1's SysNet Global example, moving from external discovery into actual server-side log reading. Recaps the principle: only log into the server once external checks (MX record, port reachability) confirm the problem is internal. Once logged in, first identify the mail platform running (checking running processes for Postfix vs. Zimbra vs. qmail -- Zimbra always runs on top of Postfix) before touching logs, since Zimbra's Postfix-derived mail log (`/var/log/zimbra.log`, referred to as "mail log") is the key artifact, rotated daily with roughly 4 days retained by default (older logs must be pulled from dated/rotated files if the issue is older). Demonstrates actually searching the log with `grep`/`cat` for a sender domain to confirm mail was received, then explains Zimbra's internal mail-tracing pattern in detail: Postfix accepts an inbound message and assigns it an internal queue/message ID; that message is handed to Amavis (running on the Postfix-Amavis integration, itself wrapping ClamAV for antivirus and SpamAssassin for spam scoring) for antivirus/anti-spam scanning; once Amavis clears the message ("passed clean"), Postfix picks it back up under a *new* message ID (since it now moves to an internal delivery queue) -- so tracing a single email end-to-end in the logs requires following the ID chain from the original SMTP-accepted ID through to this second internal ID; final local delivery happens over Postfix's LMTP protocol on port 7025 into the user's actual mailbox, and once that final "sent via LMTP" line appears for a given message ID, delivery is confirmed successful with nothing further to look for. Notes this Amavis-based two-ID tracing pattern is specific to Zimbra environments; plain Postfix (without Zimbra) doesn't generate this secondary internal queue ID, making its logs comparatively simpler to trace. Explicitly calls this pattern "very critical" and pauses to check the trainees understood it before moving on.