Unable to receive emails from friends

 This week I became aware that a contact has been receiving my emails but is unable to reply or send me any email. I am only aware of this one person but there may be more. I am receiving emails so not all my contacts are being blocked. Checked my blocked list, my filter settings and my junk folder. Nowhere is there an indication that this friend should be blocked. Normally I receive emails from her every day...and did so through last week. What more can I do!? Apparently I am not alone in this issue.....