The name or address of the mail server (SMTP server).
This property specifies the IP address or domain name of the mail server. It must be set before a connection is attempted and cannot be changed once a connection is in progress.
If this property is set to a domain name, a DNS request is initiated.
If the connection is configured to use a SOCKS firewall, the value assigned to this property may be preceded with a "*". If this is the case, the host name is passed to the firewall unresolved and the firewall performs the DNS resolution.