(if you're using apache), check that the LimitRequestBody directive isn't
set too low (it's optional, so it may not be there at all).
+process_links: follow redirects and save all available file information
+ (mimetype, date, size, oembed, etc.). Defaults to true.
file_quota: maximum size for a single file upload in bytes. A user can send
any amount of notices with attachments as long as each attachment
is smaller than file_quota.