What are the actual attachment limits?
Gmail accepts attachments up to 25 MB and switches to a Drive link above that. Outlook.com allows 20 MB, and Microsoft 365 mailboxes are often set to 25 MB by an administrator. iCloud Mail allows 20 MB. Many corporate gateways are stricter, and some sit at 10 MB.
The limit applies to the encoded message, not your file. Attachments are base64-encoded, which adds about 33%, so a 20 MB PDF arrives as roughly 27 MB of message. Aim a comfortable margin below the stated cap — under 18 MB for a 25 MB limit.
Limits were checked against each provider’s own help pages on 2026-09-20. Administrators can set lower ones, and often do.
Fix one: compress to a target
Set the target to the number you need — 10 MB, 5 MB, 2 MB — and let the tool work down to it. For a report full of photos or a scanned bundle, getting under 5 MB usually costs nothing you can see.
This is the right first move because it keeps the document as one file, which is what the recipient wants.
Fix two: split it into parts
When quality must not change — a print-ready file, a signed original, a technical drawing — split by size instead. Each part is filled to just under the limit you set, so you send the fewest attachments possible.
Name them clearly and say in the email how many there are: "1 of 3" in the file name saves a round of questions.
Fix three: zip it, or send a link
A ZIP saves little on a PDF that is mostly images — the data is already compressed — but it does bundle several files into one attachment, which gets around per-attachment limits and keeps an order.
Above 25 MB, a link is the honest answer: your own cloud storage, a file transfer service, or the provider’s built-in large-file handling. Zip first if the files are numerous, and consider adding a password to the PDF if the link will be forwarded.