DNN 8 users cannot reset their password - dotnetnuke

Question

I have a DNN 8.0.1 website
The users are not able to reset their own passwords. There is an error generated when the reset email is sent:
Mailbox unavailable. The server response was: 5.7.0 Mail relay denied
[...]. Invalid credentials for relay for
Emails are sent through an SMTP relay handled by G-Suite.
here is the stack trace:
at System.Net.Mail.MailCommand.CheckResponse(SmtpStatusCode statusCode, String response)
at System.Net.Mail.MailCommand.Send(SmtpConnection conn, Byte[] command, MailAddress from, Boolean allowUnicode)
at System.Net.Mail.SmtpTransport.SendMail(MailAddress sender, MailAddressCollection recipients, String deliveryNotify, Boolean allowUnicode, SmtpFailedRecipientException& exception)
at System.Net.Mail.SmtpClient.Send(MailMessage message)
at DotNetNuke.Services.Mail.Mail.SendMailInternal(MailMessage mailMessage, String subject, String body, MailPriority priority, MailFormat bodyFormat, Encoding bodyEncoding, IEnumerable`1 attachments, String smtpServer, String smtpAuthentication, String smtpUsername, String smtpPassword, Boolean smtpEnableSSL)
I have tested the SMTP settings at both the Host and Site Admin levels and they both work.
Email generated from other services are working and emails generated from custom modules are working. Just the emails being set for password resets are not working.
Does anyone have an idea as to why this is happening?
Thanks

Answer 1

When you send an email using the SMTP test, are you sending to an address in the domain of the server? That should work because it doesn't involve a relay.
For relaying, it is the To email address that counts. Relaying means that you are sending to an address that is outside of the domain of the website. So, you need to have permission to do that.
Are your users possible at external email addresses?
One other thing to look at is the SMTP setup for both Host and Site. If I'm remembering right, DNN8 lets you set up separate SMTP for the Host and the site. You may want to check these.
Finally, the way to really see what is going on is to see what is sent to the SMTP server. If you can get at, or have someone get at, the SMTP logs, you'll see exactly how you are sending and the exact error. Given that you are using G-Suite, this may not be easy.
You may get more information from the log4net logs. If there is nothing useful there, you might want to (temporarily) adjust the logging level.
Are you able to get a password reset message for your account?