restricting email receipts
Is It possible to make an email address that will only accept mail received from parties that use a certain subject line?
For example: an email account has been set to only accept mail that has a subject line that starts with **
SUBJECT: long time no see
this is not allowed to be received by you email account.
But - SUBJECT: **long time no see would be received by your email account.
Obviously this is a very simplified example, more complex requiem is desirable.
If this is possible - How?
Any suggestions, answers or advice is hugely appreciated.
Thanks to all respondents.