How early do I need to send scores?

I’m planning on retaking the subject tests in December. In order to get these to colleges for the January 1st deadline, would I have to have them sent automatically before seeing the scores?

In other words, do the sat scores need to physically be at the college by January 1st, or do they just need to be sent/postmarked by the 1st?

I can’t seem to find a clear answer on this, and I am not really comfortable sending my scores without seeing them first.

Thank you.