Generally, 18 U.S.C. § 3237(a) provides that in cases where the offense was begun in one district and completed in another, venue may be laid in any district through which the offense was continued. Section 1341, however, has its own "built-in" venue provisions. The locus of the offense under section 1341 has been carefully specified; and only the acts of "placing", "taking" and "causing to be delivered" at a specified place have been penalized. Venue should therefore be placed according to the specific prohibitions of section 1341, irrespective of section 3237(a). See Travis v. United States, 364 U.S. 631, 636-37 (1961) ("[V]enue should not be made to depend upon the chance use of the mails, when Congress has so carefully indicated the locus of the crimes."). The locus for mail fraud prosecutions is specifically set forth in section 1341; since Congress has "otherwise expressly provided," section 3237 is inapplicable to mail fraud.
Accordingly, venue must be charged in either (1) the district in which the letter was placed in the mail by the defendant; (2) the district in which the defendant took or received the letter from the mails; or (3) the district in which the defendant knowingly caused a letter to be delivered according to the direction thereon. Hagner v. United States, 285 U.S. 427 (1932)); see also United States v. Turley, 891 F.2d 57, 60 (3d Cir. 1989) (government conceded that section 3237 is not applicable to mail fraud).
Several decisions, citing as authority the provisions of section 3237(a), have held that venue for mail fraud prosecutions also lies in any district through which the count letter passed. Section 3237(a) must, however, be read in light of the constitutional requirements and the explicit provisions of section 1341. See JM 9-43.300 (Statement of Policy concerning Venue in Mail Fraud Prosecutions).