Sendmail - No route to host
We have a Red Hat Linux server that sends email out daily. It points to and Exchange server for smtp. It works fine, however, at least once a day, an email will fail and in the maillog I see "No route to host". After a few minutes, everything is working fine. The Linux server and Exchange are on the same VLAN and IP subnet. Anyone have any ideas why this could happen?
Do you receive a bounce back on the linux server or is the only evidence in your maillog file?
Assuming it is sendmail that is your MTA, it will defer the email for a few minutes and try again. So eventually your email is delivered.
Try a few things,
I'd create a script to ping the exchange server from your linux server and send the output to a log file. Any evidence the physical connection is faulty?
Create a script to resolve the Exchange server's hostname, domain MX record endlessly. If the "No route to host" occurs at the same time every day then have the script run an hour before up until an hours after that designated time. It is possible your linux server can't resolve the Exchange server's hostname or MX record.
Thanks for the suggestion. I'll give this a shot and see what happens tonight. I'll keep you posted.
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