Yahoo, iCloud, Proton and Zoho: Attachment Limits Compared

Gmail gets most of the attention, but a large share of the world sends mail through Yahoo, iCloud, Proton, or Zoho. All four cap attachments somewhere between 20 and 25 MB — and the difference that actually matters is not the number.

It is what happens when you go over. Some providers quietly convert your attachment to a cloud link and the message goes through. Others simply refuse, usually with an error that does not explain why.

The limits side by side

The "~" column is the honest one. Every provider measures the encoded message, not the file on your disk, and base64 encoding adds roughly a third. A 25 MB cap is reached by a file of about 18 MB — less once you count the body text, your signature, and any inline images.

Yahoo Mail: the hard stop

Yahoo's help documentation states plainly that the sum of all attachments in a single message must not exceed 25 MB.

What makes Yahoo frustrating is the absence of a graceful fallback. Gmail will offer to swap an oversized attachment for a Google Drive link; Outlook does the same through OneDrive. Yahoo just refuses the message. If you are a Yahoo sender, the entire burden of fitting under the limit falls on you.

Practically: assume 18 MB, and if the recipient is unknown, assume 10 MB.

iCloud Mail: 20 MB, or 5 GB if you are careful

Apple caps standard iCloud Mail attachments at 20 MB and offers Mail Drop for anything larger, which uploads the file to iCloud and sends a link supporting up to 5 GB.

Mail Drop is genuinely useful and it has three catches worth planning around:

• The link expires. The recipient gets a download link, not a file. If they do not fetch it in time, it lapses.
• It is not an attachment. For anything the recipient needs to archive, forward, or print later, a 20 MB attachment is better than a 5 GB link.
• It depends on your recipient's patience. Some people simply will not click a link in an email, and you cannot blame them.

For most document workflows — a signed form, a statement, an application PDF — the right move is to compress the file under 20 MB and send it as a real attachment, keeping Mail Drop for the genuinely huge files that cannot be reduced.

Proton Mail: asymmetric by design

Proton publishes its limits separately by direction: 25 MB outgoing, 50 MB incoming, with a cap of 100 attachments per message.

Two things follow from the encryption model. First, the limit includes the message body, so a long message eats into your attachment budget. Second, attachments count against your storage quota on paid plans in a way that plain links do not. Higher tiers raise the ceiling considerably.

Zoho Mail: depends entirely on your plan

Zoho's help documentation states that for personal users the maximum email size, including all attachments, is 20 MB. Organisation users are different in two directions: administrators can lower the ceiling through a Mail Policy, and paid plans raise what you can send by attaching files as links instead.

Two details worth knowing:

• The error is "Mail Policy Violation". If Zoho refuses a message with that wording, the attachment size — yours or a limit your admin set — is the usual cause. Zoho does not fall back to a link automatically on the free tier.
• The 20 MB is measured after MIME encoding. Zoho's documentation notes that attachments are MIME-encoded per the RFC standards before sending, which is the same base64 inflation described above. A 20 MB cap fits a file of about 14 MB on disk.

Paid users hit the limit far less often because the composer offers to attach oversized files as a link. If you are on a free or organisation account and the file must arrive as a real attachment rather than a link, keep it under 14 MB — see the section below.

What to do when the file will not fit

If you are sending through a messaging app rather than email, check the separate WhatsApp, Telegram and Slack PDF limits.

The options are the same across all four, and the order matters:

1. Confirm the actual size. File properties, not a guess.
2. Compress locally in the browser. Open the compress tool and reduce the file. Your document is processed on your device and never uploaded, which matters when it is a bank statement, a contract, or a medical record.
3. Reduce the source when you can. A 200 DPI grayscale scan of a text document is dramatically smaller than a 600 DPI colour scan of the same page, and usually just as readable.
4. Fall back to a link only for files that must not change. Signed PDFs, fillable forms, and certified documents should go as links or as-is — not through a compressor.

The one number to remember

If you send to people whose provider you do not know, keep the file under 10 MB.

That single rule clears every provider in the table with margin to spare, survives encoding, and leaves room for a signature with images. It also happens to be easy to hit: most text documents and well-scanned pages land well under 10 MB without any real effort.

Official sources

• Yahoo: message size limits in Yahoo Mail
• Apple: mailbox size and message sending limits in iCloud
• Proton: attachment and email size limits
• Zoho: attachments in emails

Providers adjust these limits and restructure plans. Check your provider's own page before relying on a number that matters.

Before you hit send

• ☐File is under 18 MB for a 25 MB provider, under 14 MB for a 20 MB provider
• ☐Under 10 MB if the recipient's provider is unknown
• ☐Message body, signature, and inline images accounted for
• ☐The document is not digitally signed and not password-protected
• ☐You checked the downloaded copy opened correctly
• ☐The original file is still on your disk