E-mail attachment
From Wikipedia, the free encyclopedia
An e-mail attachment (or email attachment) is a computer file which is sent along with an e-mail message. The file may be sent as a separate message, but now it is almost universally sent as part of the message to which it is attached. Attached messages may be sent in unencoded form, or encoded in a number of ways: base64, binhex, uuencoding, quoted-printable. In MIME, the standard Internet e-mail format, messages and their attachments are sent as a single multipart message, usually using base64 encoding for non-text attachments.
Worms and viruses are often distributed as attachments to e-mail messages. With vulnerable e-mail programs the virus may be activated by viewing or previewing the message; more robust programs only allow infection if the user opens the attachment for execution. Unexpected e-mail with attachments should always be considered suspicious and dangerous, particularly if not known to be sent by a trusted source.
Some mail services and software filter out potentially dangerous attachments such as executables and scripts, although more expert users may find this limitation a nuisance. Viruses in attachments to or the body of e-mail may be scanned for and dealt with by anti-virus software running on the host computer, mail client software, and mail and Internet service providers, although non-detection of a virus does not guarantee a message to be safe.
Mail services have a limit on the size of messages which may be sent and received; this limit may restrict the size of files to be attached. Messages of excessive size will usually be returned to the sender as undeliverable. This usually happens to attachments with a total size of over 30 MB.
