Offer letter through mail

What are the conditions/terms in your offer letter?  You need to take a print of the mail and take advise of a good lawyer of your area.

Whether you have received a hard copy of offer letter or through email is immaterial. Both will have similar value and consequence.

You have not posted the complete facts.

Due to present circumstances, there may be a delay in receiving such hard copy through post/courier.  You can send acceptance also on the line.   Members can not assure you on future course of such a process by the employer..  As per my knowledge, even if you fail to report, it is not going to make any difference to your employer, as they may keep someone on the waiting list till the fill such vacancy.  An employer is really interested in getting things done without any litigation, and no genuine employer engages with legal fights and wastes his time, energy, and money.

Offer of a job is an offer till it is accepted by you irrespective of the fact that it was a hard or soft copy. Now you are to decide which one suits you

What is your dispute / problem for consideration and obligation ?