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Imap Connections Remain In CLOSE_WAIT (Doc ID 2765846.1)

Last updated on OCTOBER 11, 2023

Applies to:

Oracle Communications Messaging Server - Version 8.0.2 and later
Information in this document applies to any platform.

Symptoms


After upgrading to Messaging Server version 8.0.2.5.0 (from 8.0.2.0.0), an issue was observed where the IMAP servers stopped responding after some time.
The platform is comprised of 12 backend servers. When trying to connect to a mailbox through IMAP, it was noticed that the backend server the user was hosted on initiates a connection to an account named "admin" on all of the other backend servers.
That "admin" account is hosted on only one mailhost server only, so the other mailhosts respond with "Store Debug: User admin not on this mailhost" and then the connection stays open and is not reused.  This behavior was observed each time an imap connection was made on a mailbox.  In all cases, the imap connections stayed open until the backend server was no longer responding.

The opened imap connections between the backend servers can rise up to 16,000 connections. They stay with the status of ESTABLISHED, and then CLOSE WAIT.

A pstack of imapd during the time of the issue shows:

 

<above sequence repeats itself>

Changes

 

Cause

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