Inherited ISP host configuration nightmare

[Gene Grimm]

Upon reviewing host configurations created by my predecessor, I
inherited a nightmare. DNS was misconfigured from the start, causing
dial-up clients to use a SMTP/POP3 hostname of "domain.com" instead of
"mail.domain.com". We need "domain.com" to resolve to the NT web server
for "http://domain.com"; requests and to the Linux mail server for mail
client software. It will take a few months to migrate clients to a new
SMTP/POP3 host name. Does anyone know how to best handle this on the
Linux host in the interim? Many thanks in advance for any assistance.