90 day reporting can be done by registered mail, you can download the form here:
1. Include a photocopy the id/photo page of your passport
2. Photocopy of current visa
3. Photocopy of departure card
4. Photocopy of last entry stamp
5. Original of receipt of last 90 day notification (be sure to keep a copy for your records)
6. Completed 90 day notification–be sure to sign it (and keep a copy for your records)
7. A stamped, self addressed envelope (10 baht) to have your receipt of notification mailed back to you.
You must mail the 90 day notification to your local Immigration office. Be sure to allow at least one week for processing so be sure to mail it in plenty of time. If you are late your 90 day reporting must be done in person so that you can pay the fine of 2000 baht. If you are arrested and have not reported every 90 days, the fine is 4000 baht.
The first application for extension of stay by the foreigner is equivalent to the notification of staying in the Kingdom over 90 days. If you leave the country, the 90 day report must be made 90 days from the date of your arrival back into Thailand.