Editing Training 2022 Linux team/ (section)

==Training on Mail Sending & Receving Problem & Bouncing Problem Part-3 . Dated 03 Feb 2022 - Tetra Support Staff - Biswajit Banerjee==

{{#ev:youtube|ouqCXw0vhg8|640}}

'''Video summary:''' "Training Sending,Recieveing Bouncing Part3" -- continues the series, shifting from receiving-mail diagnosis to sending-mail diagnosis, which the presenter notes is harder because outbound problems can't be fully diagnosed from outside. Covers checking domain expiry as a first, quick external check for both directions (using `whois` locally or via web tools -- domain expiry is rare but cheap to rule out) and confirming the mail server itself is reachable (ping/traceroute/login) as a sign of whether the issue is DNS/domain-level or server-level. The core topic of this part is Tetra's outbound mail-relay architecture and why it's necessary: many cloud/hosting ISPs (Google Cloud, DigitalOcean, and others) block direct outbound SMTP (ports 25/587/465) to prevent spam abuse, while a few (Linode, AWS) allow it. For platforms that block outbound mail, Tetra runs its own relay servers (built on plain Postfix, not Zimbra) hosted on an ISP that does allow outbound SMTP, and binds them to non-standard, harder-to-block custom ports (e.g. 588, 589) that the client's mail server relays through instead of sending directly -- illustrated with a live diagram of a Zimbra server on GCP (where outbound 25 is blocked) relaying mail out through one of these dedicated relay servers. Notes this relay setup is standard for most of Tetra's hosted mail environments but not universal -- it depends on the specific customer/hosting arrangement, and briefly mentions there are three relay servers in total (consistent with the "server-relay1/2/3" setup described in other Zimbra-architecture videos on this wiki).