long ago the system.net mailsettings were used for password recovery and registration confirmation but not in quite a while. Those settings are not used anywhere in mojoPortal, only the settings in user.config are used.
If Contact Form email works then other emails should also work. Make sure you have a valid email address in Site Settings for the default from address.
email failure doesn't always result in an error message, lots of mail servers work as a queue and accept the relay but then when they process the queue they could still reject the message for various reasons like the from address is not valid. Only certaint kind sof errors result in an actual error being logged, like if the mail server refuses the connection or if it can't connect to the mail server it will generally log an error.
Also your isp can also block smtp traffic on port 25 which may not result in an error since the local machine smtp server accepts the message but it gets blocked upstream by the isp. isps often do block smtp because lots of spam is sent from compromised machines and to curb that many isps only allow you to relay mail through their own mail servers and they have restrictions to limit the volume of mail sent.