You try to attach a large file to an email and get an error message about the file size. Or you send a document and the recipient says they cannot open it. Or you attach the wrong version of a file and do not realize it until after you have sent the email.
Sending files by email seems simple, but a few small mistakes can cause real problems. Here is how to do it right.
Common file-sending problems
Most file-sending problems fall into a few categories:
The file is too large. Most email providers have a limit on attachment size — usually around 10–25 MB. If your file is larger than that, the email will not send.
The recipient cannot open the file. If you send a file in a format the recipient does not have software for, they cannot open it. A .pages or .keynote file might not work for someone using Windows.
The file name is confusing. If you send a file called “Document.pdf” or “Untitled.docx,” the recipient has to open it to know what it is. If they receive many files from you, they will not remember which “Document.pdf” is which.
You attach the wrong version. If you have multiple versions of a file on your computer, it is easy to attach an old one by mistake.
Choosing the right file format
Before you send a file, think about what format the recipient needs.
PDF is the safest choice for documents that do not need to be edited. It looks the same on every device and does not require special software to open.
Word (.docx) is the standard for documents the recipient needs to edit. Most people have Microsoft Word or can open .docx files in Google Docs.
Excel (.xlsx) is the standard for spreadsheets. Like Word, most people can open these.
Images should be sent as JPEG or PNG. These formats work on every device and do not require special software.
Avoid sending files in formats that require specific software, like .pages (Apple Pages), .keynote (Apple Keynote), or .psd (Photoshop), unless you know the recipient has that software.
Checking the file size
Before you attach a file, check how large it is. If it is over 10 MB, consider whether the recipient’s email provider can handle it.
On Mac: Right-click the file and select “Get Info.” The file size is listed under “General.”
On Windows: Right-click the file and select “Properties.” The file size is listed under “General.”
If the file is too large, you have a few options:
Compress the file. On Mac, right-click and select “Compress.” On Windows, right-click and select “Send to > Compressed (zipped) folder.” This reduces the file size, though it might not be enough for very large files.
Use a file-sharing service. Upload the file to Google Drive, Dropbox, or OneDrive and share the link in your email instead of attaching the file. This is the best option for files over 25 MB.
Split the file. If you are sending a large document, consider splitting it into two parts and sending them in separate emails. This is not ideal, but it works in a pinch.
Naming the file before sending
Rename the file before you attach it. A good file name tells the recipient what the file is without them having to open it.
Instead of: Document.pdf
Write: johnson-project-report-2026-05.pdf
Instead of: Untitled.xlsx
Write: q2-budget-draft.xlsx
Instead of: IMG_4521.jpg
Write: office-floor-plan.jpg
Keep the name short, use lowercase, and avoid special characters. If the recipient is saving your file to their computer, a clear name makes it much easier to find later.
What to write in the email
Do not just attach a file and hit send. Write a few lines explaining what the file is and what you want the recipient to do with it.
A simple email might look like:
Subject: Johnson project report — draft for review
Hi Sarah,
Attached is the draft report for the Johnson project. Please review sections 2 and 3 and let me know if you have any changes. I would like to finalize it by Friday.
Thanks, Alex
This tells the recipient what the file is, which parts to focus on, and when you need a response. Without this context, the recipient has to guess what you want them to do.
When to use a link instead of an attachment
Sometimes sending a file as an attachment is not the best option. Consider sharing a link instead when:
- The file is too large to attach. Upload it to a cloud service and share the link.
- The file will be updated. If you are working on a document with others, sharing a link to the live version means everyone always sees the latest version.
- You want to control access. Some cloud services let you set permissions — for example, you can let someone view the file but not edit it.
- You are sending the same file to many people. A shared link is easier to manage than attaching the same file to 20 emails.
When you share a link, make sure the recipient has permission to access it. A common mistake is sending a link to a file that is private, so the recipient gets an “access denied” error.
Related guides
- How to Write a Clear Email Subject Line — writing subject lines that tell the recipient what is in the email
- How to Reply When You Need More Time — what to say when you cannot send the file right away
- How to Name Files Clearly — naming files so the recipient knows what they are getting