My friend sent me a letter from the states but he didn't put my full address. He forgot to include the sub soi. For example, if I lived on Thonglor, Soi 8. He only put Sukhumvit 55, but didn't include Soi 8, however he did put my house number. Does anyone know if this letter would still get delivered?

It might be sitting in a local post office nearby. I would check after a reasonable length of time and ask about your mail. I sent a properly addressed letter to a friend in Udon Thani and he didn't get it delivered like he normally would. He finally checked at the local post office and there it was waiting for him. Sorry we can't be of more help.