SBC outgoing mail failure
Last Monday (2005 Mar 7) I discovered that my e-mail agent could not reach port 25 on either of the two machine via which the agent usually sends mail.
The sbcglobal.net still worked.
I asked for help from each of the operators of those two machines.
One of them suggested that SBC-DSL service had recently blocked outgoing port 25 access by their customers, presumably to thwart zombie machines sending spam.
When I called SBC they quickly admitted the change and told me how to unblock my port.
That took a few hours to take effect but it now works again.