Editing Training 2022 Linux team/ (section)

==Training  Genral Discussion for Mail Bounce. Dated 09 Feb 2022 - Tetra Support Staff - Biswajit Banerjee==

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'''Video summary:''' "Training Genral Discussion for Mail Bounce" -- a wrap-up/general-discussion session for the bounce-diagnosis series, working through several real support-ticket examples pulled live from the presenter's mailbox. Opens with a client-specific policy note: a client called "GoodLife" is the sole exception permitted to use IMAP (allowed because they carry very large mailboxes, up to ~70GB) while every other customer ("MotorCorp" and others) must be configured on POP3 with a 15-day server-side retention limit -- a useful concrete policy to know before troubleshooting a client's mail-client configuration complaints. Walks through several real bounce/undelivered-mail tickets and how to reason about each: a "triple bounce" case traced to a customer's own script/PHP code failing to send correctly (requiring back-and-forth log correlation between the customer's app logs and Tetra's server logs, since the fault could be on either side); a case where the *receiving* server explicitly denies mail by policy (meaning the customer needs to be told to contact the recipient's admin, since Tetra's side has no control over another organization's denial policy); a case where Outlook itself reports the sending error, meaning the diagnostic path is straight to Zimbra's own logs to find the real underlying cause (possibly a Zimbra/Postfix-level CBPolicyd restriction misconfigured for that domain); and a broader "mail bouncing from all domains" case root-caused to the customer changing their router/outgoing IP without notifying Tetra, so the new IP wasn't allow-listed on Tetra's relay servers -- fixed live by adding the new IP to the relay's Postfix "networks" allow-list file and re-running `postmap`, with the presenter stressing that customers changing their outbound IP without notice is a recurring, easily preventable cause of sudden full-domain bounce issues.