How Does E-Mail Work Through The Device - ZyXEL Communications P-873HNUP-51B Support Notes

P-873HNUP-51B Support Notes
What is the difference between the internal IP and the real IP from my ISP?
Internal IPs is sometimes referred to as virtual IPs. They are a group of up to 255 IPs
that are used and recognized internally on the local area network. They are not
intended to be recognized on the Internet. The real IP from ISP, instead, can be
recognized or pinged by another real IP. The Device works like an intelligent router
that route between the virtual IP and the real IP.

How does e-mail work through the device?

It depends on what kind of IP you have: Static or Dynamic. If your company has a
domain name, it means that you have a static IP address. Suppose your company's
e-mail address is xxx@mycompany.com. Joe and Debbie will be able to send e-mail
through the device using jane@mycompany.com and debbie@mycompany.com
respectively as their e-mail addresses. They will be able to retrieve their individual
private and secure e-mail, if they have been assigned the proper access right.
If your company does not have a domain name, it means that your ISP provides you
with a dynamic IP address.
Suppose your company's e-mail address is mycompany@ispname.com. Jane and
John will be able to send e-mail through the device using
"jane"<mycompany@ispname.com> and "john"<mycompany@ispname.com>
respectively as their e-mail addresses. Again, they will be able to retrieve their
individual private and secured e-mail, if they have been assigned the proper access
right.
Is it possible to access a server running behind SUA from the outside Internet? If
possible, how?
Yes, it is possible because the device delivers the packet to the local server by
looking up to a SUA server table. Therefore, to make a local server accessible to the
outside users, the port number and the inside IP address of the server must be
configured.
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