cyrus-sasl API change for SMTP in kmail causes brokenness (Bug #432)
SMTP authentication breaks with "E-mail sending failed: Failed to transport message. An error occurred during
authentication: SASL: successful result:"
In short - if no auxprop mechanism is compiled into cyrus-sasl from 2.1.25 forward, simple authentication breaks causing havoc in spells that rely on cyrus-sasl to provide authentication services.
The universal resolution is to downgrade to 2.1.23. Some reports suggest that if the local hostname resolves correctly to IP address that SASL will properly work, but I have been unable to duplicate that using 2.1.25.
2.1.23 works in either case.