From your Converting Characters From Legion Remix article:
- Non-Remix items will be retained and sent to your mailbox; this includes Non-Remix Artifact Weapons you unlocked by completing the campaign quests
Blizzard, Free Trial accounts cannot open mail and retrieve the Legion artifact weapons, please add another way or method to retrieve the Legion artifact weapons once Legion Remix ends like instead of using the mail, putting the Legion artifact weapons directly into character’s backpack or another solution.