I run a mail server using no-ip, how does this effect the mailhost config that SC has since my ip is not always the same?
Thanks for your help.

Mailhost also tags the domain and usually the server names that are being used so it may not be an issue. You should try to register it and then do some extensive testing to be sure things work properly, specifically after an IP change.

and just how does a mail server actually work with no IP address? Connections have to be made somehow, and if the Internet is use, there's an IP address involved.

Not really having a clue as to what you might actually mean by a "no-ip mail server" .. it's pretty hard to say.
In general, I'd start with "it sounds a bit dangerous" ....

Google just turned up this: No-IP - Dynamic DNS, Static DNS for Your Dynamic IP http:/ /www.no-ip.com/

In that case, my answer is probably accurate, however, it is still dangerous as Wazoo mentions. Also, unless you are using a smarthost from your ISP for outgoing messages, you are likely to get a large number of rejected emails using a dynamic IP for a mail server. That is one of the first lookups on most mail servers... no static ip = no acceptance.

You'll want to bear in mind that many ISPs block mail if it originates from an SMTP server that is using a dynamic ip address. You may want to route your outgoing mail through your own isp's server to overcome that.

Andrew

There are ways Wazoo. I run a mailserver at home because I can't stand RoadRunner's mail service. I have it setup using a dynamic DNS service, so incoming mail can find the server. The trick is outgoing, since most mail servers won't accept connections from dynamic IP space. To get around this, you can setup to smarthost through another mailserver if you have one available. Smarthosting through RoadRunner's mailserver worked, but put me back in the boat of their incompetance at keeping their servers off BLs, so I ended up setting up my real mail server at work to allow me to do secure relaying through it. Works like a charm, and has for over a year.