The feauture you use for this is 'masquerading'
in your sendmail.mc you add these entries and make a new sendmail.cf
file probably (m4 < sendmail.mc > /etc/mail/sendmail.cf )
FEATURE(`masquerade_envelope') dnl
FEATURE(`genericstable',`hash -o /etc/mail/genericstable.db')dnl
GENERICS_DOMAIN_FILE(`/etc/mail/generics-domains')dnl
then you need 2 files
/etc/mail/generic-domains put here 'tinymaze2.com' this
way sendmail knows on what domain to operate
in /etc/mail/genericstable you make a table of this this
username publicname
===============
myUser
myUser@tinymaze.com
makemap hash genericstable < genericstable
will give you a genericstable.db that will be used
by sendmail. Maybe there are shorter ways, but here you can
give users even an email address outside your domain.
more info on:
http://www.sendmail.org/m4/masquerading_relaying.html