Title of admission email
If admissions are handed in by email, they will probably have a dedicated email address for admissions.  Just title your email with your name, the programme you are applying for, and an indication that it is an application, such as:


  Application of Shahryar Rah for the PhD programme in Unicorn Ethology


The rest doesn't matter, as soon as they start processing your application they are unlikely to record the title of your email.  All relevant information should be contained in the content of your application.