Create a ZIP for Email Attachments — Stay Under Size Limits
Email attachments have strict size limits: Gmail allows up to 25 MB, Outlook.com allows up to 20 MB, Yahoo Mail allows up to 25 MB. Corporate email systems are often more restrictive — 10 MB or even 5 MB per message. And many email systems block specific file extensions (.exe, .bat, .js, .dmg) as a security measure.
Creating a ZIP solves both problems simultaneously: it reduces total size through compression and bundles everything into a single .zip attachment that's universally accepted.
How much smaller will the ZIP be?
This depends heavily on file content: - Plain text, source code, CSV — 60–80% smaller. A 10 MB code project might ZIP to under 2 MB. - Office documents (DOCX, XLSX) — 5–20% smaller. DOCX files are internally ZIP-compressed already, so there's limited headroom. - JPEGs and MP4 videos — Almost no reduction. These formats use their own compression. A 15 MB batch of JPEGs will still be close to 15 MB as a ZIP. - PNG images — 5–15% reduction typically. - PDF files — Varies widely. An uncompressed PDF might shrink 30%; a scanned-image PDF might not shrink at all.
Blocked file types — Email systems block dangerous file extensions to prevent malware delivery. Common blocked types include: .exe, .bat, .cmd, .vbs, .js, .jar, .dmg, .app, .msi. ZIPping these files doesn't always bypass the block — some email filters scan inside ZIP archives. However, ZIPping is still worth trying; many filters don't inspect ZIP contents at depth.
Naming your ZIP — Name your ZIP descriptively before downloading from FastZip — the download filename becomes the attachment name. "project-deliverables-march.zip" is clearer than "archive.zip" for your recipient.
Format & Feature Reference
| Email Provider | Max Attachment Size | ZIP Accepted |
|---|---|---|
| Gmail | 25 MB | Yes |
| Outlook.com (personal) | 20 MB | Yes |
| Yahoo Mail | 25 MB | Yes |
| Apple iCloud Mail | 20 MB | Yes |
| Corporate Exchange (typical) | 10–20 MB | Yes (often) |
| University email (typical) | 5–25 MB | Yes |
| Gmail (Google Workspace) | 25 MB | Yes |
When a ZIP Still Won't Fit — Alternatives
If your ZIP is still too large after compression (a common situation with batches of photos or video), consider these approaches:
Split into multiple emails — Send 2–3 smaller ZIPs across separate emails. Most recipients prefer this to a cloud storage link.
Use "Send large files" in Gmail/Outlook — Gmail integrates with Google Drive for files over 25 MB (it converts to a Drive link automatically). Outlook integrates with OneDrive similarly. These options appear when you try to attach a file that's too large.
WeTransfer or similar — WeTransfer.com allows free transfers up to 2 GB (free tier). The recipient gets a download link rather than an attachment.
Creating a ZIP on Corporate Mac or Windows for Outlook
On managed corporate machines, right-click ZIP compression may be disabled or missing. Outlook on Windows has no built-in ZIP creation. FastZip works in Edge or Chrome on any corporate machine without admin rights.
Create your ZIP in FastZip, save to Downloads, then attach from Downloads in Outlook or your corporate email client. This avoids the need for any IT-approved software.