Why does the postmaster return an e mail with attachments?

I attached three pages, they were under the 20MB allowed but were still returned.

Why does the postmaster return an e mail with attachments?
because some systems have a firewall that will either return or hold such e-mail until the message is released by the recipient, or the recipient tells the postmaster to allow the messages from certain senders through. The fact that a lot of viruses are sent via attachments could be the reason that such things aren't trusted.
Reply:You may have a 20 MB limit, but if the recipient has a lower limit (say 2 MB for example) then HIS postmaster will bounce it back.