Editing Training 2022 Linux team/ (section)

==Training on Mail Sending & Receving Problem & Bouncing Problem Part-1 . Dated 01 Feb 2022 - Tetra Support Staff - Biswajit Banerjee==

{{#ev:youtube|mc7qlMP9GeM|640}}

'''Video summary:''' "Training Sending,Recieveing Bouncing part1" -- a clear, well-structured English-language training session on the methodology for diagnosing mail sending/receiving/bouncing issues, using SysNet Global as a running example. The central teaching point: a support engineer should NOT jump straight to logging into the server -- first understand exactly what the customer is reporting (not receiving mail vs. sending bounces vs. sent-but-not-received-and-not-bounced are three different problems needing different investigation paths) and understand how mail is supposed to flow for that specific domain, since 40-60% of issues can be diagnosed or at least narrowed down without ever logging in. Walks through the actual discovery process: use `host`/`nslookup` (both Linux and Windows CMD demonstrated) or a tool like MXToolbox to find a domain's MX record and confirm where mail is actually supposed to land; check whether port 25 (SMTP) on that mail server is even reachable via telnet, since a dead SMTP port typically means the whole world can't reach that server (a different problem shape than one-off delivery failures); and cross-check by asking the customer to test sending to an external address like Gmail to isolate whether the problem is inbound-only, outbound-only, or both. Only once external factors (DNS/MX/port reachability) are ruled out does the engineer log into the server itself -- at which point the priority is knowing what platform is running (Zimbra/Postfix account for the large majority of environments, with a small remainder split between Kloxo -- a free cPanel-like panel for small/shared customers -- and a handful of consulting-only environments) and reading the relevant logs. Ends mid-session (to be continued in a Part 2) citing time constraints, having covered the discovery/triage methodology but not yet reached the actual server-side log-reading portion.