In January, according to the New York Times, the NYC public school system — the largest in the U.S. — joined the latest educational technology bandwagon and spent $1.3 million to buy 2,000 iPads for classroom use.

On Nov 10., the Department of Education’s IT department slammed on the brakes.

In a memo addressed to all the city’s principals, deputy CTO Tom Kambouras warned that due to the proliferation of iPads, iPod touches and Android devices, the department’s wireless network — a Microsoft (MSFT) Exchange system running ActiveSync — was approaching its resource limits. Drastic action was required.

“As of Thursday, November 10th,” he wrote, “no additional users will be allowed to receive email via NYCDOE’s Exchange ActiveSync… There will be no exceptions to this policy.”

In addition to e-mail, ActiveSync provides wireless push synchronization of contacts, calendars and other tasks. Users trying to configure tablets on ActiveSync with their DOE username and password after Nov. 10 triggered an “Unable to verify account” error message.

As result, some teachers who had purchased new iPads for their classrooms canceled their orders.

Technically, the ActiveSync ban applies to Google (GOOG) Android tablets as well as iPads, but we haven’t heard any teachers complaining about having to return a shipment of Samsung Galaxy Tabs.

Tablets that are already configured are exempt from the new rules, as are BlackBerries and BlackBerry PlayBooks, presumably because they bypass ActiveSync.

A spokesman for the NYC Department of Education, which serves 1.1 million students in more than 1,700 schools, said that the new rules should only affect staff members, not students, and that the department is working on an fix. According to the DOE’s helpdesk, upgrading the department’s Exchange servers could take “an indeterminate amount of time.”

Apple (AAPL), which has pushed hard to get iPads in students’ hands, had no immediate comment.

Below: The text of the DOE memo.

Sent: Thursday, November 10, 2011 6:46 AM
Subject: Important Information about iPad and Android like devices

Dear colleagues,

Over the last several months, we have seen a proliferation of mobile type devices such as the Apple iPad, the iTouch and Android being introduced into the DOE environment. While these devices are changing the way we do our business, it has also presented us with a few IT challenges as well. One of the more significant challenges is the impact that configuring these devices to receive NYCDOE email is having on our Microsoft Exchange environment. Our Exchange system is currently operating near its resource limits and in order to prevent Exchange from exceeding these limits, we need to take action to prevent any more of these devices from being configured to receive email. As of Thursday, November 10^th no additional users will be allowed to receive email via NYCDOE’s Exchange ActiveSync.

Please note, this notice does not apply or affect Blackberry devices, the Blackberry Playbook or if you have an iPad, iTouch or Android device and it is already configured to receive DOE email via ActiveSync. This change will only apply to new user devices being introduced into the DOE environment. Due to the limitations that we are dealing with there will be no exceptions to this policy.  If you acquire a Mobile OS device and want to retrieve your DOE email you will need to do so via your mobile OS browser using OWA (see link below).

https://mail.nycboe.net

We are working on a plan to upgrade our Exchange environment to alleviate this situation and will continue to provide you with updates as more information becomes available to us.

If you do attempt to configure your new device for DOE Exchange ActiveSync, you will be prompted with an “unable to connect error” or “Unable to verify account information” after typing in your username and password. This is due to the fact that ActiveSync is disabled and cannot resolve your credentials.

As always we thank you for your patience and understanding.

Tom Kambouras | Deputy CTO
Department of Education