Email Attachment Size Limits and How to Send Large Files

Most major email services limit attachments to roughly 20–25 MB per message, and attachments grow by about a third when they are encoded for sending. In practice, keep the total of your attachments under about 15–18 MB to be safe. For anything larger, shrink the files (resize photos, rescan documents at a lower resolution) or send a sharing link from a cloud storage service instead of attaching.

Typical limits

Limits change and differ between personal and business accounts, so treat these as typical values, not guarantees:

There is a second limit people forget: the recipient's mail server. You might be able to send 25 MB, but if their company caps incoming mail at 10 MB, the message bounces.

Why a 20 MB file can fail on a 25 MB limit

Email was designed for text. To send a binary file such as a PDF or a photo, it is converted into text using an encoding called Base64, which makes it about 33% larger. A 20 MB PDF becomes roughly 26–27 MB in transit, which is over a 25 MB limit. That is why the safe working number is well below the advertised limit.

Option 1: Make the files smaller

Usually the best solution, because smaller files are also easier for the recipient to open on a phone.

Photos:

• Resize to about 1600–2000 pixels on the long side and save as JPEG at 75–85% with the Image Compressor. Phone photos of 3–5 MB typically drop to a few hundred kilobytes each.

Scanned documents:

• Rescan at 150–200 DPI in greyscale rather than 600 DPI colour, which often cuts the size dramatically.
• If the scan came from phone photos, compress the photos first and rebuild the PDF with Image to PDF.

PDFs from software:

• Try the PDF Optimizer, which re-saves the structure and shows real before-and-after sizes. In our test, a 120-page text PDF went from 66 KB to 42 KB. It does not shrink images, so for image-heavy PDFs use the steps above.

Our guide on getting a PDF under an upload limit walks through these fixes in order.

Option 2: Split into several emails

If the recipient needs the files attached, for example for a formal submission, split them:

• send documents in logical groups ("1 of 3: identity documents"), each well under the limit;
• split a long PDF into parts with Split PDF, naming them clearly.

Option 3: Send a link instead

Cloud storage services (Google Drive, OneDrive, Dropbox, iCloud) let you upload once and send a link. This is best for very large files, videos and folders of photos.

• Check the link's sharing setting: "anyone with the link" vs "only specific people".
• Set an expiry date if the service allows it.
• Tell the recipient what to expect: "I've shared a 150 MB folder with the photos via Google Drive."

Option 4: ZIP files (limited help)

Zipping groups several files into one attachment, which is tidy, but it barely reduces the size of PDFs, JPEGs or videos, which are already compressed. Some company filters also block ZIP attachments. Zip for convenience, not for size.

Sending sensitive documents

Large attachments are often things like bank statements, contracts or ID scans. If the content is sensitive:

• add a password with the PDF password tool and send the password by phone or text, not in the same email;
• prefer shared links restricted to the recipient over "anyone with the link";
• double-check the recipient's address before sending.

See how to send sensitive documents safely for more.

Working out how big your attachments really are

Before you attach anything, check the actual sizes rather than guessing:

• Windows: right-click the files in File Explorer and choose Properties. Selecting several files at once shows their combined size.
• Mac: select the files in Finder and press Cmd+Option+I to see a combined size.
• Phone: the Files app (iPhone) or a file manager (Android) shows each file's size in its details.

Then multiply the total by about 1.35 to estimate the size in transit. If the result is close to your provider's limit, shrink something before you send, rather than finding out from a bounce message an hour later.

What a bounce message tells you

When a message is too large, you usually get an automatic reply within minutes. Look for phrases like "message size exceeds fixed maximum message size", "552" or "message too large". The important detail is which server rejected it:

• If your own provider refused it, the email never left. Shrink the files or use a link.
• If the recipient's server refused it, your provider accepted it, but their limit is lower. Ask them what size they can receive, or send a link.

Some company systems quietly strip large attachments or hold them in quarantine without a bounce. If an important message gets no reply, a short follow-up asking whether the attachment arrived is reasonable.

A checklist before you press Send

1. Total attachment size under about 15–18 MB.
2. Files named clearly, e.g. Lastname_Passport.pdf.
3. Combined where the recipient expects one file (Merge PDF).
4. Sensitive files protected, password sent separately.
5. A short line in the email body listing what is attached.