I manage a group and I added one of my alternative email addresses as another subscriber, after running into problems posting to the group from my smart phone which has a different email address.? Then I discovered that there is an alias option for groups.io, so I deleted the other subscriber address. However, when I tried to add that alternative address as an alias, I am getting a failure message saying that the email address is already registered.? Can you help me sort this out so I can register the alternative address as an alias?