Given that answerers know about the subjunctive mood, they're right to tell you that in that particular sentence the clause modifies 'condition' only.
However, in general, a sentence of the form you're asking about is ambiguous. The writer may mean for the clause to modify all the items, and was just sloppy about expressing it. Often one can make the distinction based on context, especially due to pauses and intonation in conversation.
There are a few ways one can rephrase such a sentence to eliminate this ambiguity:
Reorder the List Items
If the clause modifies only one item, reorder the items so that it is clear.
The subjunctive mood is the verb form used to express a wish, a suggestion, a command, or a condition that is contrary to fact.
The subjunctive mood is the verb form used to express a condition that is contrary to fact, a wish, a suggestion, or a command.
Break it Up
If the clause applies to all the list items, break it apart from any of them.
The post office returns packages, letters, or postcards with wrong addresses.
The post office returns items with a bad address, which might be packages, letters, or postcards.