Stronger security is required
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An email attachment is a computer file sent along with an email message. One or more files can be attached mail showing attachments as binary code any email message, and be sent along with it to the recipient. This is typically used as a simple method to share documents and images. A paper clip image is the standard image for an attachment in an email client.
Email standards such as MIME don't specify any file size limits, but in practice email users will find that they can't successfully send very large files across the Internet. The result is that while large attachments may succeed internally within a company or organization, they may not when sending across the Internet.
As an example, when Google mail showing attachments as binary code Gmail service increased mail showing attachments as binary code arbitrary limit to 25MB it warned that: Note mail showing attachments as binary code all these size limits are based, not on the original file size, but the MIME -encoded copy.
A lot of malware is distributed via email attachments with some even considering such to be the main vector for cyberattacks on businesses. Email users are typically warned that unexpected email with attachments should always be considered suspicious and dangerous, particularly if not known to be sent by a trusted source. However, in practice this advice is not enough — "known trusted sources" were the senders of executable programs creating mischief and mayhem as early as with the mainframe-based Christmas Tree EXEC.
Now, many block certain types of attachments. Text files were emailed by including them in the message body. In the mid s text files could be grouped with UNIX tools such as bundle   and shar shell archive  and included in email message bodies, allowing them to be unpacked on remote UNIX systems with a single shell command.
Attaching non-text files was first done in by manually encoding 8-bit files using Mary Ann Horton 's uuencodeand later using BinHex or xxencode  and pasting the resulting text into the body of the message. When the "Attachment" user interface first appeared on PCs in cc: Modern email systems use the MIME standard, making email attachments more utilitarian and seamless.