Can I submit my first 90-day report via registered mail in Thailand?

yep filing by mail counts and you can do the first report by mail no problem

but

it takes 4 to 6 weeks to get the receipt back in the post.

You have to send in copies of:

*data page of your passport

*PDF print out of your visa

*most recent entry stamp

*TM30 receipt

Also a filled out TM47 (notification of 90 day report)

AND

a self addressed stamped envelope (so they can send the receipt of reporting back to you)

You send all that stuff Thai Post EMS (tracked mail) to this address

𝟵𝟬 𝗗𝗮𝘆𝘀 𝗥𝗲𝗽𝗼𝗿𝘁 𝗦𝗲𝗰𝘁𝗶𝗼𝗻, 𝗜𝗺𝗺𝗶𝗴𝗿𝗮𝘁𝗶𝗼𝗻 𝗗𝗶𝘃𝗶𝘀𝗶𝗼𝗻 𝟭,

𝗖𝗵𝗮𝗹𝗲𝗿𝗺𝗽𝗿𝗮𝗸𝗶𝗮𝘁 𝗚𝗼𝘃𝗲𝗿𝗻𝗺𝗲𝗻𝘁 𝗖𝗼𝗺𝗽𝗹𝗲𝘅 (𝗕 𝗕𝘂𝗶𝗹𝗱𝗶𝗻𝗴),

𝟭𝟮𝟬 𝗠𝗼𝗼 𝟯, 𝗖𝗵𝗮𝗲𝗻𝗴𝘄𝗮𝘁𝘁𝗮𝗻𝗮 𝗥𝗼𝗮𝗱, 𝗦𝗼𝗶 𝟳,

𝗧𝗼𝗼𝗻𝗴𝘀𝗼𝗻𝗴𝗵𝗼𝗻𝗴, 𝗟𝗮𝗸𝘀𝗶 𝗕𝗮𝗻𝗴𝗸𝗼𝗸, 𝟭𝟬𝟮𝟭𝟬

One last thing, the packet you send to them EMS tracked mail has to be post marked at least 14 days before your due date

You can do by mail first time.