You could resign in ways other than submitting a formal resignation letter. As noted earlier, not every job requires a formal resignation letter. Sometimes a conversation will suffice. You could ...

When you decide to quit a job, most companies require you to submit an official letter of resignation ... you as part of your resignation message. Close with a formal sign off, such as "Sincerely ...

one of the initial tasks is to submit a formal resignation letter to the current employer. Typically, these letters express gratitude to supervisors and colleagues for their support and guidance ...