On Fedora the virtusertable and virtual-domains files are pre-configured. On Debian you must add the following lines to your sendmail.mc file:

FEATURE(`virtusertable', `hash /etc/mail/virtusertable')dnl
VIRTUSER_DOMAIN_FILE(`/etc/mail/virtual-domains')dnl

After adding these two lines create the virtusertable and virtual-domains files using nano:

sudo nano /etc/mail/virtusertable

Save the file and exit by pressing control “o” and then control “x”. Do the same for the virtual-domains file, and them you can populate both accordingly. The virtusertable is highly useful if you are hosting multiple domains (virtualhosting). You will be able to configure multiple email addresses, at multiple domains, to be forwarded to a particular local user.