サインアップ時の問題 - プライマリメールが既に取得済みです

I recently created a forum where I sent my friend email invites. He has more than 1 email registered to the same domain, named as follows:

When I sent him the invites as bulk invite, he was only able to register from the first email and Discourse showed the following error when he tried signing up with the last email on this list:

Validation failed: Primary email has already been taken.

TIA for any help resolving this issue!

「いいね!」 2

See if you have site setting normalize emails enabled.

「いいね!」 3