Here in the southern USA many of my clients used DSL from Bellsouth and happily sent mail via mail.bellsouth.net as a smarthost. SME of course is happy to do this. After the AT&T acquisition of Bellsouth, AT&T started requiring increasing numbers of users to move away from mail.bellsouth.net and to smtp.att.yahoo.com or fmailhost.isp.att.net. These hosts require SMTP authentication.
However, as noted elsewhere in the forums, SME tries "CRAM-MD5" authentication and fails when this is not implemented on the AT&T side.
To make a long story short, I just got SME 7.4 to send via AT&T smarthost like so:
In server manager, set outgoing mail host to fmailhost.isp.att.net and do NOT use ":465" to override default port. Set username & password appropriately; in my case I had to remember to append "@bellsouth.net"
At console, issue command:
config setprop smtp-auth-proxy PeerPort 465
This worked!
AT&T actually urges you to use smtp.att.yahoo.com but that server refused with "553 From address not verified" as of course SME was sending email from my client's own domain, not sbcglobal or bellsouth or any of the others under the AT&T brand.
I'm sure there are other ways this could have been done, but this *worked*.
I'll open a bug if the developers think it would be useful.