Well, now we are back to the original question. Postal regulations say max 30 days. As for misdemeanor, where can we find that? I don't see it in postal regulations, so I would classify it as an infraction, which the new reference to the US Code would say is max $5000, yes. The misdemeanor was significantly more.
For the classification of a federal crime please see...
See 18 U.S.C. §3559(a)
http://www.law.cornell.edu/uscode/text/18/3559
(a) Classification.— An offense that is not specifically classified by a letter grade in the section defining it, is classified if the maximum term of imprisonment authorized is—
(1) life imprisonment, or if the maximum penalty is death, as a Class A felony;
(2) twenty-five years or more, as a Class B felony;
(3) less than twenty-five years but ten or more years, as a Class C felony;
(4) less than ten years but five or more years, as a Class D felony;
(5) less than five years but more than one year, as a Class E felony;
(6) one year or less but more than six months, as a Class A misdemeanor;
(7) six months or less but more than thirty days, as a Class B misdemeanor;
(8) thirty days or less but more than five days, as a Class C misdemeanor; or
(9) five days or less, or if no imprisonment is authorized, as an infraction.
Classification based on fine see first:
http://www.law.cornell.edu/uscode/text/18/19
U.S. Code › Title 18 › Part I › Chapter 1 › § 19
18 U.S. Code § 19 - Petty offense defined
As used in this title, the term “petty offense” means a Class B misdemeanor, a Class C misdemeanor, or an infraction, for which the maximum fine is no greater than the amount set forth for such an offense in section 3571 (b)(6) or (7) in the case of an individual or section 3571 (c)(6) or (7) in the case of an organization.
Then:
http://www.law.cornell.edu/uscode/text/18/3571
(b) Fines for Individuals.— Except as provided in subsection (e) of this section, an individual who has been found guilty of an offense may be fined not more than the greatest of—
(1) the amount specified in the law setting forth the offense;
(2) the applicable amount under subsection (d) of this section;
(3) for a felony, not more than $250,000;
(4) for a misdemeanor resulting in death, not more than $250,000;
(5) for a Class A misdemeanor that does not result in death, not more than $100,000;
(6) for a Class B or C misdemeanor that does not result in death, not more than $5,000; or
(7) for an infraction, not more than $5,000.
