pegasus wrote:

Is an SMTP server address 3 numbers.3numbers.3numbers.2numbers?

No. It can be xx.x.x.xxx as well. Each octet can be in the range 0 to 255
(with some exceptions). It can also be a fully qualified domain name, like
smtp.somemachine.somedomain.com or .net. In fact, a FQDN is much much more
common than a specific IP address. The latter will always work. The
former, though, may not. Suppose, for example, your ISP's SMTP router is
named "smtp.bigdomain.net" and, up until now, the IP address for that
machine has been 62.1.16.4. Now suppose that your ISP wishes to use a
bigger, faster machine for mail routing. One thing they might do is to
modify their Domain Name Service (the service that maps FQDNs to IP
addresses) to make "smtp.bigdomain.net" point to the IP address of that
bigger, faster machine, say 62.1.16.10. If you're using a FQDN in your
account settings, your email keeps working. If you have the IP address of
the old machine in your account settings, your mail stops working and you'll
have no idea why.
--
Brian Tillman