Email attachment size limits: every major provider in one table

As of October 2026, the usual email attachment size limit is 25 MB at Gmail, Outlook.com, Yahoo Mail and Proton Mail, 20 MB at iCloud Mail, and 35 MB by default for business mailboxes on Microsoft 365. Most of these limits cover the whole message, text and attachments together, and some count the attachment after it has been encoded for email, which makes it about a third bigger.

Below is the reference table, built from each provider’s own help pages, followed by the reasons a file can bounce even when it looks under the limit, what each service does when you go over, and the options that work for bigger files.

Attachment size limits by email provider

Sources: Google, Microsoft, Yahoo, Apple, Proton, Zoho, Fastmail, GMX, WEB.DE and Orange help pages, consulted in October 2026. Company mailboxes can be configured differently by their administrators, so treat these as the defaults you are most likely to meet. Note that Microsoft’s own pages are not fully consistent: an older general article still mentions 20 MB for Outlook.com, while the current Outlook.com page says 25 MB.

Why does an attachment bounce when it looks under the limit?

Email was designed for text, so every attachment is converted into text with an encoding called Base64 before it travels. Base64 turns every 3 bytes into 4 characters, which makes the attachment roughly 33% bigger inside the message. Microsoft documents that increase for Exchange, and Google’s Workspace documentation counts about 37% on received mail.

Whether that matters depends on how each server measures. Google states that its Workspace sending limits apply to the content before encoding, whereas its receiving limits and Microsoft’s message size limits count the encoded size. Microsoft gives a concrete example: with a 64 MB limit, expect a realistic maximum of about 48 MB of attachments. Since you rarely know how the recipient’s server counts, the safe rule is to assume the overhead.

The recipient’s limit counts too

An email has to be accepted by two servers: yours when you send, and the recipient’s when it arrives. If your provider lets a 30 MB message through but the recipient’s company server stops at 20 MB, the message bounces, sometimes with a “message size exceeds fixed maximum” error, sometimes silently. Organisations set their own caps, and security gateways may also strip or quarantine attachments. Even Microsoft notes that messages leaving its datacenters max out at about 112 MB once encoding is added, whatever the configured limit. When you write to someone for the first time, assume the lowest common denominator: around 20 MB, or less.

Gmail attachment size limit

Personal Gmail accounts can send up to 25 MB of attachments. If you add more, Gmail removes the attachment and inserts a Google Drive link instead. The file is then stored in your Google account (15 GB free, shared with Gmail and Google Photos), and you need to check the sharing permissions so the recipient can open it. Google Workspace has the same 25 MB sending limit on most plans, up to 50 MB on Enterprise Plus from the web. Gmail also blocks certain file types, such as executables, even inside ZIP archives. Step-by-step options are on our page send large files with Gmail.

Outlook and Microsoft 365 attachment size limits

There are three situations to keep apart. Outlook.com (including Hotmail and Live addresses) accepts messages up to 25 MB, text and attachments included, and lets you attach OneDrive files as links of up to 2 GB that do not count toward the limit. Microsoft 365 business mailboxes, on Exchange Online, default to 35 MB for sending and 36 MB for receiving, and an administrator can set anything between 1 MB and 150 MB; Outlook on the web allows 25% less than the configured setting, and the Outlook mobile apps stop at 33 MB. Finally, the Outlook desktop app has its own default of 20 MB for internet accounts such as Gmail or IMAP mailboxes. More details and workarounds: send large files with Outlook.

Yahoo Mail, iCloud Mail and Proton Mail

• Yahoo Mail: the sum of all attachments in one message must not exceed 25 MB, for incoming and outgoing mail alike.
• iCloud Mail: 20 MB per message. Apple Mail can switch to Mail Drop, which uploads attachments of up to 5 GB to iCloud and sends a link that expires after 30 days; Mail Drop files do not count against your iCloud storage, within a 1 TB Mail Drop allowance.
• Proton Mail: 25 MB of attachments when sending, 50 MB when receiving, up to 100 files per message. For larger files, Proton suggests a Proton Drive link, which can have a password and an expiry date.

Why do email providers limit attachment size?

Email copies every attachment into every recipient’s mailbox, through every server on the way, and keeps it there until someone deletes it. A 100 MB file sent to ten people becomes more than a gigabyte of stored and transferred data, multiplied by every forward and reply-all. Size caps keep mail servers fast, limit storage costs and reduce the room for malware. That is also why links have become the standard for anything big: the file is stored once and downloaded only by the people who need it.

What to do when an attachment is too large

1. Use your provider’s link feature: Google Drive in Gmail, OneDrive in Outlook, Mail Drop in Apple Mail, Filelink in Thunderbird. Easy, but it uses your cloud storage and the recipient may have to request access.
2. Send a transfer link: upload the files to a transfer service and paste the link in your email, or let the service email it. With Transfr, up to 100 GB per transfer is free and the recipient needs no account.
3. Compress only if it helps: text-heavy files shrink, but photos, videos and PDFs barely change. See should you zip files before sending?.
4. Split the email: several smaller messages work for a handful of documents, but they are error-prone beyond that.

Our page on sending large files by email walks through these options step by step, the page on sending files larger than 25 MB focuses on that exact threshold, and how to send large files compares every method beyond email.

Attachment limits in chat and work apps

Our guides to the WhatsApp file size limit and the Discord file size limit explain the details, including when photos and videos get compressed.

How to avoid bounced attachments

• Keep attachments under about 18 MB in total for most providers, and under 14 MB for iCloud Mail or other 20 MB mailboxes.
• Do not attach executables or scripts, even zipped: most providers block them.
• For a new contact at a company, assume their server is strict and send a link for anything over a few megabytes.
• If a message “disappears”, check for a bounce notice (non-delivery report) and ask the recipient to look in spam or quarantine.
• For confidential files, a password-protected or end-to-end encrypted transfer is safer than an attachment that stays in mailboxes indefinitely.