“Re:” in Letters and Email
In a formal business letter, “Re:” can introduce an optional reference line identifying the file, invoice, matter, or subject. Government of Canada guidance gives the form “Re: Invoice 62395” and notes that a Subject line can be used instead. Email reply prefixes are a separate system convention.
In a letter, “Re:” means the line is identifying what the correspondence concerns. Use it only when the document format or house style calls for a reference line.
Key details
Important caveats
Email Boundary
A manually written Re: reference line and an email client’s reply prefix are not automatically the same editorial decision.
Further guidance
Format
The reviewed government example uses “Re:” followed by a colon and the reference information.
Letters
Canada’s Language Portal describes Re: as an optional reference line in business letters.
Practical Application
Use a “Re:” reference line in a letter when the document format or house style uses one to identify the matter being discussed; place a concise subject after it.
Reader Check
Check whether the format actually calls for a reference line. Do not add “Re:” merely as decoration, and do not assume a letter reference line has exactly the same function as an email client’s automatic reply prefix.
Worked Example
“Re: Lease renewal for 18 Market Street” gives the reader a concise matter reference before the body of the letter.
Sources and evidence
Sources are shown with the role they play in this guide. Historical or style-sensitive claims are kept within the evidence boundary described above.
- Business letters: Reference line (opens in a new tab)Government of Canada Language Portal · Canadian government guidance for Re: reference lines in business letters