Sendmail relay through ’smarthost’ requiring authentication
To get sendmail to relay thru a smarthost that requires authentication, in /etc/mail/sendmail.mc
define(`SMART_HOST’, `host.to.relay.thorugh.com‘)dnl
In /etc/mail/access:
AuthInfo:host.to.relay.thorugh.com "U:username" "I:username" "P:password" "M:PLAIN"
Activate the changes
make service sendmail restart