How to configure sendmail for relaying mail over port 587 using authentication.

Solution Verified - Updated -

Issue

  • Need to setup sendmail host to relay SMTP to ISP domain. Received the following error while testing a mail delivery :

    user@xxxx.com... Connecting to smtp.<hostname>.com. via relay
user@xxxx.com... Deferred: Connection reset by smtp.xxxx.com.

Port 25 is blocked at mail server, it only accepts port 587.

Setup requirement in this server is,

  • This server (Local sendmail server) will receive mails from internal application (SAP) via port 25.
  • After receiving the mail from application, this server should relay the mail to the ISP which is smtp.XXX.com.
  • The local sendmail server should only do mail forwarding from application.

Environment

  • Red Hat Enterprise Linux
  • sendmail

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