said by NormanS:said by koitsu:I'm still trying to wrap my brain around why SMTP AUTH is required for sending mail through their mail servers on port 587. Internet folks (non-Comcast customers) cannot connect to Comcast's outbound mail servers, and Comcast will always know who sent mail through their servers based on IP number, so I'm baffled at the purpose.
Actually, we
can connect to 'smtp.comcast.net'. And, if we have Comcast account login information, we can even use those servers ("we" being people with non-Comcast IP addresses).
AFAIK, Comcast ACL determines whether authentication will be required on a port 25 connection, or not. However, authentication on a port 587 connection is an option, per RFC 2476, and designed to allow off-network access to the server.
EDIT: Oops! 
I completely misunderstood what you were saying here, Norman. I realise now you were talking about non-Comcast IPs being able to talk to smtp.comcast.net (presumably used for Comcast customers on laptop who roam, and don't want to have to change their mail client settings every time).