An email attachment is any file that is sent with an email. A file or files can be attached to an e-mail message and sent together to a recipient. Such system is usually used as an easy way to share files and photos and documents.
Originally, SMTP Internet email was only ASCII 7-bit text. Text files sent via e-mail included the text of the message. In the mid-1980s, it was possible to bundle text files with UNIX tools such as package and shell file and include them in the body of email messages, thus allowing them to, with a single shell command, be unpacked on remote UNIX systems.
Non-text files were first attached in the 1980s by manually encoding 8-bit files with uuencode of Mary Ann Horton then using xxencode or BinHex and pasting the resulting text into the message body. When around 1985 the user interface for "Attachments" were first used on computers in cc:Mail, it used the uuencode format to send SMTP, and Microsoft Mail later followed suit.
Modern email systems make use of the MIME standard, which makes email attachments more seamless and intuitive. This was developed by contributor Ned Freed and Nathaniel Borenstein and the standard was officially released in 1996 as RFC2045.
With MIME, the message and every of its attachments are combined into one multipart message, with encoding of base64 used in converting binary to 7-bit ASCII text, or on certain modern mail servers, with the option of full 8-bit support via the extension called 8BITMIME.
The size of the email when sending and receiving can have limits, it all depends on what means you are sending your email. From time to time we encounter this issue where customers ask for help when their email appears to be down. They will often say "I can receive emails, but I don't think I can send emails."
Why is there a limit to the attachment size?
Email standards e.g. MIME do not set any file size limits, but in reality email users will observe that that they cannot send very large files over the Internet successfully. This is due to a number of possible limits:
Mainly for security reasons, every email service providers limit the maximum amount of email attachment size an email account can receive. If there is no maximum limit to email size, the email server may run the risk of bombardment with very large emails, thus causing it to stop functioning properly.
Some other reasons are:
• Mail systems sometimes limit arbitrarily the volume that their users can send.
• The message often passes via different mail carriers before reaching the recipients. Each of those must store the message before it can be forwarded, thus size limits can also be imposed.
• The mail system of the recipient can reject incoming emails that contain attachments of more than the file size limit.
Certain providers of free email address also impose commercial limits on email size: the free account has a low email size cap, but by upgrading to a paid account you can increase the cap.
Mail store size control:
If there is no limit on the size of the attachments, users will send very large files which will cause mass storage problems for the mail store’s back-end.
Performance:
Email systems are not designed to transfer large files. Often times, client systems download messages to the local computer. The implication is that messages and their attachments are downloaded automatically even if the user does not need the attachment. This problem is solved by dedicated file sharing systems such as DropBox by keeping the file on the server until the user makes a specific request to download them. Some email clients can be programmed to act this way. Dedicated file sharing systems make use of more efficient protocols for downloading files.
What happens is that though large attachments may be successful internally within an organization or company, they may not be successful when sent over the Internet.
For example, when Gmail increased its arbitrary limit to 25MB, google warned that users might not have the ability to send larger attachments to their contacts who make use of other email services that have a smaller attachment limit.
Also note that all of these size limits are not based on the size of the original file, but on the version encoded using MIME technology. Common Base64 encoding increases the original file size by 37%, which means that a 20MB original file can exceed the 25MB limit for attachment. The 10MB limit for email size requires attachments to be limited to around 7MB.
What happens when you reach the maximum email size?
If you send a mail whose attachment size exceeds the recipient's maximum email attachment size lime, your email will bounce and you will receive an error message in your mailbox. Typically you will receive one of the following error messages:
"The size of the attached file exceeds the permissible limit";
"552: message size exceeds the maximum allowed";
"The system could not deliver: the message size exceeds the outgoing message size limit";
“The size of the message you want to send exceeds the server’s global size limit. The message was not sent. Please reduce the message size and try again.”
Common Limits for Providers:
To help, here is a summary of the email limits of popular email services. That's what you'll find in the terms and conditions when you sign up for a service from your ISP, and we've all read it, yes.
Orcon
Orcon doesn't specifically talk about email limits, but has a "fair use" policy instead.
Gmail
Sending and Receiving Limit: 25MB (per message).
Yahoo / Extra:
Sending and Receiving Limit: 20MB (per message).
Windows Live Mail
10 GB (per email) and not more than 50 MB per attachment
Vodafone/Clearnet/Paradise:
Sending and Receiving Limit: 10MB (per message).
Hotmail/Outlook.com
Sending and Receiving Limit: 10MB (per message).
Mozilla Thunderbird
Unlimited
Can These Email Size Limits be Bypassed?
The simple answer is: No, you cannot exceed the maximum size limits. However, there are alternative solutions:
You may attempt to compress attachments, but be aware that some file formats do a better compression than others;
Some email clients can break large attachments into smaller pieces and then send them as multiple emails and recombine them at the receiving end;
The best solution is to upload the attachments to a remote storage service (such as SkyDrive, DropBox, or Google Drive and include the download link thus generated in your email.