Authentication error when sending email from workflow but list alerts email work fine

[#1]

I have a list. When a user enables alert on this list then he/she is able to receive email from SharePoint when someone adds a new item or change item.

But emails sent by Nintex workflow are not being sent. Error is:

Error 530 5.7.1 Client was not authenticated

Why emails are not being sent by workflows?

[patrick_hosch · Accepted solution]

do you experience the same issue when running SharePoint Designer workflows?

A few things to look at:

1. Make sure outgoing emails are configured and that the settings are correct
2. Review your SP log files and see if you can get a more detailed description of the error (temporarily turn up the logging level to get more details!)
3. Check that all emails are valid and they are not blocked by your SMTP admin
4. Check if your firewall or antivirus apps are blocking emails