How can I fix this error:
"421 SMTP service not available, closing transmission channel"
I am sending an email from a linux webserver using sendmail. This webserver is in the DMZ (optional interface) of a firebox 1000 firewall appliance. The exchange mail server is in the trusted network. The firebox NATs 220.127.116.11 to 192.168.1.3.
I've tried all I know on the linux side using LUSER, SMART_HOST entries in sendmail.mc, setting up the hosts file to show 192.168.16.3 goes to mail.mywebsite.com, etc.
For some reason, the mail says its unavailable for only this type of situation, otherwise it sends email out fine to other domains. BTW, the firewall routes mail.mywebsite.com to 18.104.22.168 --> 192.168.16.3 and it routes www.mywebsite.com
to the linux webserver (22.214.171.124) with no private IP.