No other email server is needed besides Xeams. In this case, users configure their email clients
such as Outlook, Mozilla Thunderbird or other to use the SMTP, POP3/IMAP server provided
by Xeams.
Xeams will be used for both inbound as well as outbound emails.
In this case, Xeams is used to filter inbound emails for another server downstream. This other server
could be any SMTP server, including MS Exchange, Zimbra, Postfix, IBM Dominos or other.
Since Xeams is only used for inbound, every outbound email is sent directly from your actual email server.