Edit Excel, Word and PowerPoint attachments without leaving Thunderbird.
A colleague sends a workbook. You press Edit in SumOffice, the attachment opens in a real editor on your own computer, and the file you save is attached to a reply — already there, waiting for you to write a line and send it. The original message and the original attachment are untouched.
What happens, step by step
- Open a message with an .xlsx, .xlsm, .docx or .pptx attachment.
- Press Edit in SumOffice. The attachment goes to the SumOffice Local program on the same computer — through Thunderbird's native messaging, not over the network.
- The matching editor opens: SumSheet for spreadsheets, SumDoc for documents, SumSlide for presentations. Macros in an .xlsm file stay in the file.
- You edit and save. Thunderbird opens a reply with the saved file attached.
- Sending is yours. The add-on never sends a message — it only prepares the reply.
Install — two steps
| 1. SumOffice Local | The program that opens the file and does the editing. Download the DMG for macOS (Apple silicon) — signed and notarized by Apple · SHA256SUMS |
|---|---|
| 2. The add-on | Until the listing is published on addons.thunderbird.net, install it from here: sumoffice-thunderbird-2026.4.2.xpi. |
Thunderbird may ask to restart after installing the add-on. No account, no key, no sign-up — neither step asks for one.
What works today
| Platform | macOS on Apple silicon only. Windows is in progress; there is no date yet, and we will not promise one here. |
|---|---|
| Formats | .xlsx, .xlsm (macros kept in the file), .docx, .pptx |
| Thunderbird | Measured on 153.3.1esr |
| What it changes | Nothing in the original message or attachment: the edited file goes into a new reply |
Where your file goes
Nowhere but your own computer. The add-on hands the one attachment you picked to SumOffice Local through Thunderbird's native messaging — a channel between two programs on the same machine. The document is not sent to SumOffice or to any other service, and there is no account to sign in to. The full statement is in the privacy policy.
If something goes wrong
Write to hello@sumoffice.com — a person reads it. The support page lists what helps us answer faster.