Although the words attachment and enclosure often are used interchangeably in business letters, they represent different methods of including items. In the strictest sense, an attachment is considered to be part of the letter while an enclosure is treated as a separate document. For some organizations, such as the government, the use for each is delineated by the correspondence sent, while for others either use is acceptable.
An attachment is a document that is part of the business letter. It adds or further describes the information within the letter. Some examples include a spreadsheet that provides a visual explanation of financial billing or forecasts, a chart that gives a graphic view of the business trends or a budget. When sending an attachment, include the word, “Attachment” on the bottom left side of the letter with a semi-colon and the number of the attachment. You should also mention in the body of the letter that an item is attached (or multiple items are attached) that enhance or further explain information in the letter .
An enclosure is a document that is in addition to the business letter. It can stand alone as its own document and does not require the business letter to explain what the document is or how to interpret it. When sending an enclosure in a business letter, place the letters “Enc” with a semi-colon or write the word “Enclosure” at the bottom of the letter on the left-hand side. Then put the name of the document. This alerts the reader that a second document is included in the correspondence. One example of a document that's appropriate for an enclosure is a resume included with a cover letter. The resume is separate from the letter and easily stands alone.
In some situations, there is no method available to differentiate between an attachment and an enclosure. One of these situations occurs when you are sending a business letter by email. Because there is no enclosure option given, and email is a form of electronic transmission, all documents sent by email become an attachment. The attachment is added to the email as a downloadable item that is sent with the body of the email.
There may be rules in place for the use of attachments and enclosures in certain federal government branches. For example, in their correspondence handbook the U.S. Geological Survey describes how to handle an attachment and an enclosure when sending correspondence to them. According to their handbook, you send an item as an attachment when the correspondence is a memo, while if it is a letter you should use the word enclosure for additional documents. In either case, type "Enclosure" or "Attachment" two lines below the signature block. Doing this tells the reader to look for the enclosures or attachments. If they are missing, ask to have them sent because they were intended to be sent with the letter or memo.
If there is more than one attachment or enclosure, indicate how many such as "2 Enclosures" or "3 Attachments." If either is not identified in the text, use a colon after the word, followed by the document's title or explanation on the next line. For example: "Enclosure:" (next line) indent two spaces and add "Resume of John Q. Adams" without ending punctuation. When there are multiple enclosures or attachments that aren't mentioned in the text, title or describe each on a separate line. For example: 2 Attachments: (next line) indent two spaces and type: "Resume of John Q. Adams" (next line) indent two spaces and type: List of Awards and Achievements" with no ending punctuation.