Configure hMailServer for domain accounts registered at 1and1

Suppose the domain name is foo.com and one wants to configure hMailServer for email account foo@foo.com

1. Create a subdomain mail.foo.com at 1and1.
2. Set the A-Record of the subdomain (mail.foo.com) to the IP address of the server hosting hMailServer (e.g. 555.555.555.555).
3. Set the Mail Server (MS Record) of domain foo.com to the subdomain mail.foo.com.
4. Create a domain in hMailServer (foo.com).
5. Create an account under the above domain (foo@foo.com)

After the above steps, email client applications (e.g. Outlook, Thunderbird) can be configured with the account foo@foo.com using mail.foo.com as both the incoming server and the outgoing server.  It is beneficial to know that mail.foo.com is essentially translated to an IP address. Incoming email (e.g. POP3) uses port 110 and outgoing mail (SMTP) uses port 25.  If hMailServer hosts email accounts for multiple domains (e.g. foo1.com, foo2.com), all the accounts share the SMTP server even they may specify the outgoing email server addresses as mail.foo1.com, mail.foo2.com because they all point to the same address. The SMTP of hMailServer is associated with only one domain because it needs to send out this resolvable domain name to prevent the receivers from perceiving the email as spam.