To add email aliases to a user, use the csattribute add -a command to add mailalternateaddress attributes to the user entry.
For example, to add two aliases for a user named John Smith with these values:
With a mail attribute of: johnsmith@sesta.com
Email aliases: johns@sesta.com and jsmith@sesta.com
The commands would look like the following examples:
csattribute -a mailalternateaddress=johns@sesta.com add johnsmith@sesta.com
csattribute -a mailalternateaddress=jsmith@sesta.com add johnsmith@sesta.com