I am writing to inform you of my resignation from my position as [job title]. Please accept this letter as formal notice that ...

Handing in a resignation letter is never easy ... circumstances may warrant a longer or shorter notice period. If you decide to quit your job a month into it, a two-week notice should allow ...

When you decide to quit a job, most companies require you ... right away and don't have time to draft a formal letter – sending a two-weeks' notice email may be appropriate.