Why does Lotus Notes prompt for authentication when displaying HTML e-mails?
Note: This Knowledge Base article references software which is not maintained or supported by Cisco. The information is provided as a courtesy for your convenience. For further assistance, please contact the software vendor.
Lotus Notes does NOT support NTLM authentication, it only supports Basic authentication.
If you configured your Identities to only use NTLMSSP, then authentication with Lotus Notes will not work. The user gets continuously prompted for authentication, even after entering the correct credentials.
In order to address this problem, you can configure the Identities to use "NTLMSSP or Basic" authentication scheme instead of NTLMSSP only.