Are you getting Error 500 when attempting to use SMTP in Options - General?

This error happens most often when attempting to use your POP 3 logon credentials for SMTP on an SMTP server which distinguishes between the two. Most SMTP servers do NOT require username or password and will error if CRD attempts to logon using these.

Try leaving the username and password blank. This resolves the issue in most cases.

If your SMTP server really does require a username and password, then ensure that you are using the correct username and password required by your SMTP server for SMTP logon.