Editing Training 2022 Linux team/ (section)

==Training on Mail Sending & Receving Problem & Bouncing Problem Part-5 . Dated 07 Feb 2022 - Tetra Support Staff - Biswajit Banerjee==

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'''Video summary:''' "Training Sending,Recieveing Bouncing part5" -- shifts to diagnosing actual bounce cases, live, on one of Tetra's real relay servers (`server-relay1.tetrain.com`, confirming there are three relay servers total as mentioned in Part 4). Opens with the retry logic behind Postfix queuing: a failed outbound message isn't simply dropped -- it retries on a roughly logarithmic backoff (e.g. ~6 minutes, then ~30 minutes, then hours, then up to a day later), and the specific error encountered determines how long the next retry waits (a temporarily unavailable server retries soon; a nonexistent domain waits much longer). Demonstrates searching the relay's Postfix mail log for "bounce" and walks through several real bounce cases found live: one where a message triggers a bounce/delivery notification for unclear reasons requiring deeper log tracing by message ID; one where a specific recipient address is explicitly rejected by the receiving mail server (meaning the sender's own admin needs to contact the receiving domain's admin, since the sending side has no control over another domain's rejection policy); and one caused by a missing/incomplete SPF record on the sender's domain -- diagnosed by pulling the domain's TXT/SPF record via MXToolbox and confirming the sending relay server's IP isn't authorized in it, which is why the receiving Gmail-side server rejected the mail as likely spam. Notes bounce causes are numerous and case-specific, and that this topic continues into the next session. Ends mid-topic due to time (session capped at ~30 minutes as usual for this series).