Nirmal J via Mailman-users writes:
If you don't mind can you please take remote access of my server through any desk or any other software and check it please.
I don't access other people's systems without a contract.
DNS Report for that list1.iitm.ac.in is 10.24.5.52
in any case, That is a non-routable address, visible only from your internal network. We cannot access it.
I don't see anything that would cause your problem in your Mailman configuration files. Again I suggest you check other HTTP applications including your webserver and any proxies between the Mailman core host and the HyperKitty host for access restrictions. You should also check the intervening network(s) for access restrictions, although I'm not sure a network access denial would result in an HTTP 403 code.
-- GNU Mailman consultant (installation, migration, customization) Sirius Open Source https://www.siriusopensource.com/ Software systems consulting in Europe, North America, and Japan