From Manuel v. State, 2011 Tex. App. LEXIS 7152 (Tex. Ct. App. Aug. 31, 2011):

An e-mail is properly authenticated if its appearance, contents, substance, or other distinctive characteristics, taken in conjunction with circumstances, support a finding that the document is what its proponent claims. See Shea, 167 S.W.3d at 105; Massimo v. State, 144 S.W.3d 210, 215-16 (Tex. App.-Fort Worth 2004, no pet.). Characteristics to consider in determining whether e-mail evidence has been properly authenticated include (1) consistency with the e-mail address in another e-mail sent by the alleged author; (2) the author's awareness, shown through the e-mail, of the details of the alleged author's conduct; (3) the e-mail's inclusion of similar requests that the alleged author had made by phone during the time period; and (4) the e-mail's reference to the author by the alleged author's nickname. Massimo, 144 S.W.3d at 215-16 (citing United States v. Siddiqui, 235 F.3d 1318, 1322-23 (11th Cir. 2000), cert. denied, 533 U.S. 940, 121 S. Ct. 2573, 150 L. Ed. 2d 737 (2001)).

Text messages can be authenticated by applying the same factors. See, e.g., Dickens v. State, 927 A.2d 32, 35-38 (2007) (threatening text messages received by victim on cell phone con-tained details few people would know and were sent from phone in defendant's possession at the time); In re F.P., 878 A.2d 91, 95 (Pa. Super. 2005) (threatening instant messages properly authenticated through circumstantial evidence including screen names, context of messages, and surrounding circumstances); see also Goode, supra, at 9. Rule 901(b)(4) has also been applied to authenticate MySpace evidence. See Tienda v. State, No. 05-09-00553-CR, 2010 WL 5129722, at *4-5 (Tex. App.-Dallas Dec. 17, 2010, pet. granted). And other jurisdictions have applied similar rules to Facebook messages. See, e.g., State v. Eleck, No. AC 31581, 2011 Conn. App. LEXIS 427, at *17-18 (Conn. App. Ct. Aug. 9, 2011) (showing that messages came from particular Face book account insufficient to authenticate messages without further "foundational proof"); Commonwealth v. Purdy, 459 Mass. 442, 450-51, 945 N.E.2d 372 (2011) (holding that e-mail sent from Face book account bearing defendant's name not sufficiently authenticated without additional "confirming circumstances").

Another traditional method of authentication permitted by Rule 901 is the "reply-letter doctrine." Varkonyi v. State, 276 S.W.3d 27, 35 (Tex. App.-El Paso 2008, pet. ref'd) (citing Cathy Cochran, Texas Rules of Evidence Handbook, Article IX, at 915 (6th ed. 2005)). Under this doctrine, a letter received in the due course of mail purportedly in answer to another letter is prima facie genuine and admissible without further proof of authenticity. Id. This doctrine applies to e-mails. Id. Therefore, an e-mail is sufficiently authenticated when a person responds to an e-mail that was sent to the person's e-mail address. Id. This rule has been applied to other types of messages by analogy. See, e.g., People v. Pierre, 838 N.Y.S.2d 546, 548-49 (N.Y. App. Div. 2007) (applied to instant message where person sent instant message to screen name and received reply, content on reply supported conclusion that message was sent by defendant, and no evidence was admitted to show anyone else had motive or opportunity to impersonate defendant by using his screen name).

Rule 901 clearly provides that the illustrations are not exclusive means of authentication. See Tex. R. Evid. 901(b) ("By way of illustration only, and not by way of limitation, the following are examples of authentication or identification conforming with the requirements of this rule[.]")