Some of the team members are not receiving any email related to task assignement/subscriptions in Rational Team Concert

We have a project my team is working on... only some of the team members never receive any email related to task/defect assignments, subscriptions and change in their defects/tasks....

while rest of the team members have no such issues. I have re checked the email configuration settings for these problematic users; these settings are exactly same as the users receiving emails....

I have also checked their email address as well...

please suggest any solution, thanks