If you need mail aliases, you need to check your MTA requirements. Smail will use /usr/lib/aliases in the form of
alias: mark, marko, mjk
Look it up for further info.
sendmail uses a similar file and format, but is usually in the /etc directory. (It could reside somewhere else depending on your configuration.)
Your configuration files for qmail and mailhandler all contain a place for you to define aliases so that if
[email protected] and
[email protected] and
[email protected] ar all the same person, mail gets directed tot he correct mailbox.
I'm not familiar with all the MTA's out there, so you may need to do more research.