* Correspondence: This is a general term for letters, especially when referring to a collection or series of them. "Your correspondence has been received."
* Communication: This is a broader term but can be used formally, especially if the letter's purpose is to convey information. "We are awaiting your formal communication on the matter."
* Epistle: This is a more archaic and literary term for a letter, often implying a more serious or significant message. It's generally only suitable in very specific contexts. "The apostle's epistle offers profound wisdom."
* Missive: Similar to "epistle," this word suggests a formal or official letter, often carrying weighty news. "The missive arrived unexpectedly."
You can also use descriptive phrases depending on the letter's purpose:
* Your official communication of [date]...
* The document dated [date]... (if it's a formal letter with official status)
* Your submission of [date]... (if it's a letter applying for something or making a proposal)
Avoid informal terms like "note," "message" (unless it's a very short, specific message), or "mail" when aiming for formality. The best choice will depend on the specific circumstances.