I am looking for ideas for a subject for an email to send my resignation letter.
Certainly! Here are some ideas for subject lines for a resignation letter email: 

1. "Notice of Resignation - {Your Name}" - This shows your intent to submit your resignation while still being professional and giving the employer time to find a replacement. 
2. "Resignation Effective {Date}" - This subject line is helpful in giving your employer an exact date on which a replacement has to be found. 
3. "Formal Resignation" - This subject line is professional and shows the formality of your resignation. It also signifies that you are not open to negotiating or discussing your resignation. 
4. "{Your Name} Resignation Announcement - This subject is useful if you have more than one party that you are sending your resignation to ensure that everyone is aware of your decision to leave. 