Is this right to say grammatically 'May I come in'?

Yes, it is absolutely right to say 'May I come in?' Using 'may', especially in the question, symbolises that the person asking the question is asking for permission to do a particular activity. Often people confuse and use 'can' instead of 'may' which is not correct. read more

Absolutely right to say"May I come in" You may observe that some people use can instead of may but the difference is that can is authoritative on the other hand may is polite and while asking for permission you want to be polite rather than authoritaive otherwise people will think ill of you. read more

Although strictly, can relates to the ability to do something, whereas may concerns permission to do something, can is often used instead of may in constructs such as the above. That works acceptably in the first person:"Can/May I [do something]". read more

Get Grammar Girl's take on can versus may. Learn whether can i go to the bathroom is acceptable, or if you should always say may i go to the bathroom. read more