UNIX for Advanced & Expert Users

I need to send mail using different gmail smtp logins, depending on the from header. I can put the appropriate expression in dc_smarthost to generate the host, but I don't know how to specify the login id. The login id comes from passwd.client and is associated with the server name. According to the documentation passwd.client is looked up using the reverse translate of the server ip, so I don't know how to use /etc/hosts tricks to create aliases.

Any suggestions as to how to accomplish this. Should I be taking a completely different approach?

I am not experienced with exim4, but I know the neighborhood. I think you might get more info by using the -bh, -bt and -d options appropriately to test your configuration and get additional information about where it looks.

Assisting DNS lookups, forward or backward, with /etc/hosts just means adding redundant lines there to support lookup that might be missing on DNS. Often a host looks up forward OK but when you get the nslookup PTR reverse lookup of the IP, the IP is tied to another name as primary, so it is misconfigured or a CNAME for the other. Proper DNS is the the A and PTR records agree, and other names on the IP are CNAME attached. One solution is to use the host name from the PTR, assuming it also has a DNS A record. Using nslookup -d2 can reveal more of the DNS configuration.