• 421 Too many concurrent SMTP connections; please try again later.

    When trying to end an emails from squirrelmail ,I got the following message :

    ERROR:    Message not sent. Server replied: Service not available, closing channel
    421 Too many concurrent SMTP connections; please try again later.

    It means that there are to many open SMTP connections either incoming or
    outgoing.The default is 20, you can raise that with the smtp_accept_max
    command in your configuration file.

    you can check connections through command:

    cat /etc/exim.conf |grep smtp_accept_max
    By default ,the value is 100 ,You can raise it to 150 then run :

    Service exim restart

    You can get all the IPs addresses connected to/from TCP port 25 at any given time by running the following command :

    netstat -plan|grep ‘:25’|grep ESTAB

     

    Categories: Exim

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