Step 1: Check if Informatica email task is able to send e-mail to your personal id. If yes that means email configuration is good and informatica admin need not to be contacted.
Step 2: Now send a test email to id which has reported the issue. If success, you can understand that recipient mailbox is not full.
Step 3: Create one personal outlook Distribution list with your email id, and send a test email through informatica, if success that means informatica email task is able to send mail to outlook distribution list.
Step 4: If all above is ok then check if you have placed space in email addresses ( ids ) list, remove space in email address list, and this should solve your problem.