noun, noun or participle which takes 'suru'
under separate cover; accompanying letter
Refers to a letter or document sent separately from the main correspondence, often in the same envelope or package. Used in formal or business contexts.
履歴書は別封でお送りします。
I will send my resume under separate cover.
請求書を別封にて同封いたします
We will enclose the invoice as an accompanying letter.