It’s not the mobile browser. Unsubscription is not possible for non logged users. For those the link unsubscription_confirm_url is not working, and the message described above is shown.
What can be done?
thanks for your reply. You are completely right. There is a security plugin installed called WP-SpamShield. When it’s deactivated the link is working fine also for unlogged users. Thank you!
Did you know about this issue before? Is there something to be done to get working both plugins?