E-mail Attachments

In short: E-mail attachments are files sent along with an e-mail. They are a common route for malware.

In more detail: Technically attachments are encoded in Base64 via MIME, which makes the mail about a third larger. Many providers limit to about 20 to 25 MB.

In Depth

Dangerous attachments

Executable files (.exe, .scr, .bat, .js), Office documents with macros (.docm, .xlsm), nested archives, ISO and shortcut files. Double extensions such as “rechnung.pdf.exe” disguise programs.

Rules

Open only expected attachments, check the sender, block macros, show file extensions, check suspicious files in a sandbox. See phishing mails, e-mail worms, Base64.

See also: Phishing Mails, E-mail Worms, Locky, Base64