You can create a text file in Postfix containing an alias email and several destination emails. There are two ways to implement aliasing and mailing list in Postfix depending on how it is configured.
For System Accounts
mydestination = $mydomainor sending to a non-existent account gives the error message
Recipient address rejected: User unknown in local recipient table
alias: address1,address2If address has the same domain as yours, you can leave it out. Thus you can use the /etc/aliases file to alias an email address or to build a mailing list.
For Virtual Accounts
virtual_mailbox_domains = $mydomainor sending to a non-existent account gives the error message
Recipient address rejected: User unknown in virtual mailbox table
postmap -q firstname.lastname@example.org /etc/postfix/valias
virtual_alias_maps = hash:/etc/postfix/valias
If you are using virtual accounts, instead of maintaining a text file containing the aliases and mailing list, it would be better if you can work with your virtual accounts source. See the links below for examples
To Test Postfix