Environment:
Secure Messaging Gateway (SMG) 7
GroupWise 18.3.1

Situation:
When users are trying to log into the SMG Quarantine page with their email address and email password, they are getting an error: Authentication failed, please try again.

Resolution:
There are multiple areas that need to be checked to ensure the users are able to log into the quarantine:

If the user account was manually created in SMG, remove the account in the SMG Admin Console | System Administration | Organization/Policy Management | Manage Users section.
In the SMG Admin Console | System Administration | Organization/Policy Management | Domain Management | <expand domain > | ensure the 'Enable user auto-provisioning' is checked.
In the SMTP Hosts section below, ensure the Security & Authentication are both set to 'auto' and the 'Auth" option on the same line is checked.

In the GroupWise Administration Console | GWIA properties | SMTP/MIME tab | ESMTP Settings | ensure the 'Require SSL for authentication' matches the SSL settings set for the SMTP port in GWIA Properties | GroupWise tab | Agent Settings.
In the GroupWise Administration Console | GWIA properties | Access Control tab | SMTP Relay Settings | if 'Prevent message relaying' is enabled, ensure in the Exceptions (Allow) there is an entry for the IP Address of the SMG server to *.

Confirm the users are now able to log into the SMG Quarantine using their email address and email password.