The Google-Yahoo poker game over e-mail storage continues. Just a week after Yahoo quadrupled the size of its free e-mail accounts to a gigabyte, Google is doubling its storage size for Gmail accounts to two gigabyes tomorrow. That’s enough for about 200,000 text e-mail messages. Better still for users, the Mountain View technology giant says it will continue to expand Gmail’s storage allotment periodically over the “coming days and months,” though it would not say by how much or how often.

“We want to change it from being a static thing to something that will grow naturally,” Georges Harik, director of Gmail, told us today.

Having pushed its free e-mail accounts from a paltry 4 megabytes to a gigabyte in the span of a year, Yahoo scoffed at Google’s latest move, and now says that mailbox size is becoming “irrelevant.”

“At a certain point beyond 1 gigabyte, it’s just a number and becomes irrelevant to most free e-mail users,” said Karen Mahon, Yahoo spokeswoman. “As an offline analogy: Going beyond a gigabyte for free is like adding a bucket of water into an ocean.”