E-mail is second only to the telephone in terms of the number of worldwide users in modern business and commerce, but it's nearly impossible to figure exactly how many emails are sent each day.

VeriSign (the exclusive registry for .com and .net domains) estimates that there are about2.25 billion email queries per day. However, because of caching, email queries represent only a fraction of the number of emails sent.  As such, e-mail often forms a significant part of large scale exercises such as discovery or disclosure. It does however have an important place in computer forensics, and is a regular method for communicating sensitive, protected or confidential information.

An e-mail trail is often a very common method for distributing intellectual property such as client lists or copyrighted material. An e-mail investigation, whether corporate email or web-based mail, (e.g. Hotmail) can be invaluable in determining a course of conduct, and in providing enough evidence to show that other systems, possibly in the control of a third party, may need to be investigated.

Internet History may reveal the how a crime was researched and possibly indicate a suspects 'mens rea' (criminal intent). In the case of web-based e-mail such as Hotmail,  actual content of messages from cached web pages may be recovered.