It is better to resign in person than by sending a formal resignation letter via email. But, if your circumstances don’t allow you to resign in person, better to send a polite and formal email resignation letter that notify your leaving date and the purpose of leaving your job.
In a company, as a new joinee, either, you receive a hard copy (printed copy) of a job offer letter or soft copy through e-mail. Your job offer letter is considered as an on-paper confirmation letter that becomes a proof of your employment. Similarly, your professional resignation letter is considered as a recorded proof that assures your resignation.
Standing Order 18 of the Industrial Employment (Standing Orders) Act, 1946 that workman has a right to resign from the services by giving a notice of the period as prescribed under Standing Order 17 which provides termination of services by serving 30 days notice upon a permanent workman and seven days notice with respect to workman who is on probation and temporary workman by serving a 24 hours notice. Thus, for a permanent employee, a period of 30 days is provided to terminate or resign as is apparent on a conjoint reading of provisions of Standing Orders 17 and 18.
Clause 2 of Standing Order 18 provides that in case resignation is submitted with immediate effect or at any time before expiry of notice period, acceptance is necessary. Acceptance of resignation is not required in case a notice has been given of 30 days. It would operative from and effective on the lapse of the period. So, giving a resignation letter becomes important as it helps you alot incase you have any differences. But if it is not mentioned in your terms and conditions of your contract that you will have to notify the company before resigning, I dont believe notice is required in that case.
Reference: Industrial Employment (Standing Orders) Act, 1946