Email Marketing Software

Thank you all in advance in taking your time.
Please read before you jump and reply to this question.
( I am a software engineer, my question is very specific, and yes, I did do a lot of thinking and searching myself before posting this question. I appreciate your time taken.)
I am looking for a email client or a software (like Mailwasher Pro) which can download emails from your service provider (for ex. gmail) and then allows the user to bounce few messages/mails – those are already been received to your inbox. I DO NOT want to set any filters. I just looking for a client/software that allows me to bounce mails at my will (not automated), Its not a hard bounce. I only just want the sender to think (or discourage) that the email account does not exist, with a standard reply gmail would give for any email send to a non-existing account.
Is any body familiar with such a software/client/application? I really do appreciate your help and time taken to address this question. Thank you again in advance.
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