Is “message too large” the sender’s or recipient’s fault?
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You sent an email and got a bounce back saying the message was too large. So whose fault is it? Honestly, it's a bit of both, but the fix is yours to make.
The recipient's mail server has a maximum message size, set by their IT team or mail provider. That limit isn't negotiable. Gmail and Outlook both cap incoming messages at 25MB. A lot of corporate servers sit at 10MB or lower. You can't change those limits from the outside, and the server won't make exceptions.
But here's the thing: you built the email. You chose what went into it. If it's too big, there's something in there that can be trimmed, compressed, or moved to a cloud link.
One detail that catches a lot of senders off guard: Base64 encoding (the way email handles attachments) inflates file sizes by roughly 33%. So a 10MB PDF becomes around 13MB by the time it travels through an email server. That's enough to tip you over a 10MB corporate limit even when your attachment looks fine on your end.
A few quick benchmarks worth knowing. Your HTML email body should ideally stay under 100KB (plain HTML, no images embedded inline). Attachments are what really push you over. If you're sharing large files, upload them to Google Drive or Dropbox and drop the link in the email instead. Recipients click through when they're ready, and you don't have to worry about server limits.
For most email, under 5MB total is a safe target. Under 25MB works for consumer inboxes. But if you're emailing corporate contacts or anyone with managed IT, assume 10MB is the ceiling until you know otherwise.
The "fault" question doesn't really help you. The server rejected your message, so the practical answer is always the same: send something smaller. That's within your control.
If you're seeing a pattern of size-related bounces across multiple recipients, it's worth auditing what you're sending and whether any of those addresses are worth reaching out to separately. You can also check our Email Header Analyzer to see exactly how large a sent message actually was, headers and all.
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