- Can I give to them your emailaddress
- May I give to them your emailaddress
Can and may are auxiliary verbs. Can is used to show the physical ability to do something while may is used to express possibility or permission.
The use of may or can depends on the situation. If you are writing a formal letter, it would be best to use may. May is just more polite, and it is also more formal.
Can is more often used in an informal siuation. Let's say you're at a cookout, and you ask, "Can I have another hotdog."
As with most writing, you need to know your audience and know what option is best for the situation at hand. Also, as a side note, you cannot use may to express an ability to do something, but you can use can in more informal situations to express permission.