I have a client using XO as their ISP. They are running SBS 2003 and are having problems sending emails to Comcast accounts. XO doesn't offer a smarthost option and doesn't have an option to add an SPF record. We have setup a RDNS record.
At this point XO is not willing, or able, to do anything more to help troubleshoot this problem. As a workaround, I configured their domain to send emails using AuthSMTP.com, which worked fine with one exception. We have a few people that have their company email forwarded to an external account. Since AuthSMTP.com requires that each sending email address is authenticated prior to being able to send, all of the forwards from domains outside of the network fail with an 'not an authorized user' error.
Ideally I'd like for this to work like all of the dozens of other SBS servers we support.
Anyone have a brilliant and cunning plan?