I will be out of town until August 22nd.
我將出差，8月22日返回。（out of town可以看作"離開狀態，出差中"的意思。用這個表達時不要忘 記寫明自己離開的時段。）
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.

感謝您聯系斯坦西斯·埃塞特拉。不過很抱歉，2月5日前我都不在公司。回來之后我將立刻查閱您的來信。謝謝您。

I will be in touch with you as soon as possible when I return.
我回來后會盡快與您聯絡。（這是表示自己一回來就會給對方回復郵件的句子。）
I will be in touch with you upon my return.
我一回來就聯絡您。
I will read your e-mail when I get back.
我回來后就看您的郵件。