How To Configure Sendmail to Forward Mails to a Relay Host aka Smarthost (Doc ID 2018587.1)

Last updated on JULY 16, 2024

Applies to:

Goal

The default sendmail.cf is set up as an MTA (mail router), using DNS to forward mails to the Mail Exchanger  (MX) record for the domainname resolution  In the event that the DNS config does not cater for public network access or does not contain valid MX (mail exchange) records for forwarding, sendmail will fallback to forwarding message to the default host named "mailhost.domainname"

Eg. /etc/mail/sendmail.cf :

O FallbackSmartHost=mailhost$?m.$m$.

 

In the absence of either mailhost or MX record in the DNS naming services, one can set up the sendmail to forward messages to a defined Mail Relay / Relayer, otherwise known as Smarthost, using this macro SMART_HOST:

define(`SMART_HOST', `<FQ_HOSTNAME>')

Solution

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