I will be out of town until August 22nd.
我将出差，8月22日返回。（out of town可以看作"离开状态，出差中"的意思。用这个表达时不要忘 记写明自己离开的时段。）
Thank you for contacting Stencils Etcetera. I'm sorry, I'm out of the office until February 5th. Your e-mail will be reviewed as soon as possible after my return. Thank you.
I will be in touch with you as soon as possible when I return.
I will be in touch with you upon my return.
I will read your e-mail when I get back.