In Harappan civilization, trading activities were in a state of flourish. That the Harappan traders had contact with Mesopotamia can be gauged from the fact that a number of Harappan seals and objects have been found in Sumer. According to experts, the land of Melukha, which finds mention in Sumerian documents, is, in fact, the land of Harappan civilization.
Lothal, Surkotda and Balakot in Indus civilization were some of the important coastal towns from where the Harappan products might have found their way to Mesopotamia.
From Mesopotamia precious metals and raw materials were exported to Indus civilization. If you take discovery of the Indus seals in Mesopotamian civilization, we can safely come to the conclusion that traders from India actually resided in Mesopotamia. It seems that cotton was the main article of export to Mesopotamia.