since upgrading to 10.21 CUP1 CM has stopped sending emails. The config is correct and the error reported is :
javax.mail.NoSuchProviderException: No provider for smtp
This could indicate that the mail jar is either missing or not in the classpath. There is another post on this subject where another customer has the exact same problem, but no answer there. Can you let us know if this is a known issue and there is a fix ? Otherwise indicate if a support case should be opened.