@kahn-hubitat would be the right person to answer this. My understanding is that his Sendmail integration works best if you use your ISP's mail server and not something like GMail. To get it work with GMail, you will probably have to subscribe to G-Suite.
Also, I'd recommend following up on the parent thread for @kahn-hubitat's app, linked below:
@jmforem - you may be able to get around this by creating an "app specific password" in your gmail profile and then using that password instead of your regular password here. I think Gmail asks you the first time to validate the account and I am not sure if this app will handle that. I don't use this app in HE, but use this approach for sending SMS from Node-RED.
To create an app specific password, go to your Google Account ->Security->Signing Into Google -> App Passwords.
Just looked at the code - it definitely uses Base64 encoding of authentication credentials (username/password), but I don't think that Hubitat's telnet implementation supports encryption.
I don't use this app in HE, but use this approach for sending SMS from Node-RED.
To create an app specific password, go to your Google Account ->Security->Signing Into Google -> App Passwords.
I when to gmail and set up the app password but not having any luck as it keeps telling me that it fail to send? Can you tell me how to set it up? Thanks
I use this via Node-RED as well (for email). I previously used it for SMS but I found that the SMS was often delayed, sometimes by as much as 30 minutes or more. I then switched to Twilio for SMS. It is pretty inexpensive unless you are sending out lots and lots of texts.
Which node are you using for sending email? I use the standard email node and below is my setup. The "password" is the app specific password in the Google account setup.