This page was last updated: 10/24/2014 11:12:58 AM I'm trying to send a large file attachment via email, but it's failing. Why?
I'm trying to send a large file attachment via email, but it's failing. Why?
Internet email systems are neither designed nor intended to move large files
around. They are designed for sending email, and optionally, an attachment of
reasonable size. Unfortunately, there is no set industry standard on maximum
message size on the Internet. Every company, organization, and Internet email
provider is free to set their own limit. Many Internet email providers set the
message size limit in the 10MB range (e.g. Hotmail). Some, including Yahoo, AOL,
and Gmail, are a little more generous and allow 25MB messages.
Note: the size limit
refers to the entire message, not just the attachment. Due to the overhead
created by MIME attachment encoding and other factors, the actual maximum
attachment size that you'll be able to send is usually somewhat less than that
limit. In other words, a mail system that allows 10MB messages will handle
attachments roughly in the 8MB range.
Our CWSL Exchange
email system allows messages up to 30MB internally as
well as out through our email gateway to the Internet. However, that doesn't
mean that the email system on the other end will accept that message, because there is no established
standard across the Internet for maximum message size. Therefore, there should be no
expectation of success when sending a large file via email, particularly if the
file is larger than 10MB. A good rule of thumb is that anything less than 10MB is
likely to be OK when sending over the Internet as an email attachment. If it's
larger than that, it can be hit or miss, so have no expectation of success of
sending an attachment larger than 10MB out to the Internet unless you know that
the recipient's email system supports an attachment of that size.
The issue of Internet email message size limit has created an opportunity for
3rd-party cloud-based systems to handle the sending of large files over the Internet. Some
that come to mind are WeTransfer.com,
Hightail.com,
DropSend.com, and
ShareFile.com. These are just a few. Just Google send large
files, and you'll find at least a dozen sites that offer this service, some for
free or with a trial account, or with a limitation on size. The general idea of
these services is that they offer a cloud-based temporary file storage location. The sender uploads the
file and is then given a URL to that file. The sender can then email this URL to
whomever needs to download the file. After X days the service will delete the
file from their system, so they are not accumulating storage obligations. These
services are simple to use and allow the transfer of huge files over the
Internet without ever impacting an email system because the file itself
is never emailed, only the URL is, which is of course very small. Using
one of these services is the recommended way to send large files to someone else
on the Internet.
If the message you are sending (or expecting to receive) does not contain a
large attachment, it could be that the attachment is of a type that is blocked
at the gateway. Many file types, including executables (.exe, .com, .vbs, etc.)
and zip files, can be malicious. These are blocked without notification to
the sender or recipient by the CWSL email gateway. Again, when
sending large attachments, or any attachment which could potentially be
malicious, we recommend using a file transfer service, like those mentioned
above.
In summary, when trying to send a large file to someone else on the Internet,
do not use email. Use one of the aforementioned 3rd-party services. If you are
trying to send a large file to someone else on the CWSL network, use a folder on
our file servers. Contact HelpDesk if you are not sure which folder is
appropriated to use.
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