Reciprocal pronouns express a mutual relationship between the subject and the object. they are used when each of two or more subjects is acting in the same way towards the other.

There are only two reciprocal pronouns, and they are both two words:   Each other  and   One another

Examples:

• John is talking to Mary, and Mary  is talking to John. So we say:

• John and Mary are talking to each other.

Uses

When we use these reciprocal pronouns there must be two or more people, things or groups involved (so we cannot use reciprocal pronouns with I, you [singular], he/she/it), and they must be doing the same thing.

Look at these examples:

• Peter and Jane hate each other.
• The three gangsters were all blaming one another.
• We gave each other gifts.
• Why don’t you believe each other?

As you can clearly see, each other is used in more examples above than one another. This is simply because in general we use each other more often than one another, which sounds a little formal. Moreover, it is often said that  one another should be used only for three or more people or things, but there is no real justification for this.