Does mail get delivered on Sundays?

I have a best friend (guy) in Georgia. We send letter to each other almost every other day. My ex bf (as of yesterday) was very controlling and tried telling me I couldn’t be friends with him. Yesterday was the last straw when he started an argument over my boss because my boss was praising my work. My best friend sent a letter, I’m not sure when it arrives but my ex was at my house today paying my mom some money for something he bought from her. He’s crazy so I’m afraid he could’ve got the letter if it was sent today