The best way to resolve this would be for the owner of the key to add another User ID with the desired email address.  Only the owner of the key can do this:  Right click on the key, select Key Properties, and select Add New Email Address at the top of the window.

On your end, you can add a new messaging policy:

If any

Recipient is <the alias email address>

Encrypt to      A list of keys

Use the Edit List button to specify that user's key.

My partner has created a PGP key with other opensource tool and has given it to me to upload it to the universal server. Is there any way to associate it with his alias email?

once you have imported the key inside pgp desktop you can add another email address to be associated with it

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