DeskNow by default supports what is sometimes called 'SMTP Journaling' - i.e. it is possible to configure DeskNow to store all incoming/outgoing emails of a domain to a particular mail account (journaling)
Optionally it is also possible to forward these emails to another server via SMTP ('push' or 'bcc' journaling). For a schematic example from Barracuda Networks (one of the best know mail archiving solution providers), see http://www.barracudanetworks.com/ns/downloads/Admin_Guides/Barracuda_Message_Archiver_AG_US.pdf (see section "Message archiving concepts").
To configure mail archiving in DeskNow, simply login as the admin user of the domain you want to manage, and click on Administration/Mail archiving.
Note that you can use a different setting for each domain, so that each domain can have its archiving solution (or no archiving).
Simply create an account like email@example.com, and set the Administration/Mail archiving option to point to it. Then configure your appliance to retrieve mails from this account (either via POP3 or IMAP).
Push or bcc journaling
DeskNow can push emails for the journaling address to a particular SMTP server. This can be the mail archiving appliance or software.
For instance, you can set mail archiving for the domain mydomain.com to go to the address firstname.lastname@example.org , where 220.127.116.11 is the IP address of your archiver appliance.
Consult your archiving appliance/software documentation for more details on what type of interface it supports.