Is “message too large” the sender’s or recipient’s fault?

"Message too large": Shared responsibility.

Recipient's constraint:

Server has maximum message size. Configured by their administrator. Cannot accept messages beyond limit.

Sender's creation:

You created the large message. Attachments, images, content. Your choice of what to include.

Practical reality:

You must adapt to recipient limits. Cannot force them to accept. Your job to stay within bounds.

Common limits:

Gmail, Outlook: 25MB. Many corporate: 10MB or less. Base64 adds ~33% to attachment size.

Solutions:

Reduce attachment size. Use file sharing services. Compress before sending. Know your audience's limits.

Fault does not matter; adaptation does. Send what recipients can receive.