Hi,
When you work in any organization, you should trust the organisation, its governance and the overall management. If you have received a communication expressed in the form of an email, you no need to worry. Also there is no point in worrying much about - whether you got one in letter head with seal and signature of the letter head because a good number of companies are stopped issuing even offer letters, performance reviews, payslips etc. in hard-copy format. More hr transaction work is happening online.
If you are having doubts about the integrity of the organisation (if the management fails to get your trust in the activities and their leadership), any validated occurrences where management breached contracts with employees/customers etc., then time up for you to search for a new job.
If you believe you are in a good company, getting salary in time, reasonably good work ambience, good ecosystem to learn etc., stay happy.No need to worry about hard copy of confirmation letter (salary credit in your bank account itself is evidence that you are working and paid by the organisation).