Not sure where I read it, but I don't believe it is legal to have a mailbox that doesn't "break away". I understand your frustration on this, but I think it's geared more towards passenger vehicles. Something along the lines of you being liable for any injuries that may occur if someone hits it.
Just did a quick search and found this, Wayne county.
MAILBOX INSTALLATION ALONG COUNTY ROADS:
The following is a summary of standards for mailbox installations along county roads. Mailboxes that are installed within the public road right-of-way are considered obstructions as they present hazards to the traveling public. Therefore, Wayne County strongly recommends the following mailbox materials and installation as recognized by the U.S. Department of Transportation (USDOT) and the Ohio Department of Transportation (ODOT). Please contact your local postmaster for mailbox location approval before actual installation.
POST MATERIALS:
1. Wood posts shall be a maximum of 4 inches by 4 inches square or 4-1/2 inches round timber. 2. Steel posts shall be a maximum of 2 inch diameter (2-3/8 inch O.D.) schedule 40 standard strength steel pipe.
3. Any material with breakaway cross section characteristics equivalent to 1 or 2 above.
SETTING POSTS:
Contact the Ohio Utilities Protection Service (1-800-362-2764) so they can notify utility members to mark their underground utilities before digging the post hole.
Posts need to be set a minimum of 2-3 feet (preferably 3 feet) from the edge of the pavement to the roadside face of the mailbox. Where curbs are present, the face of the mailbox shall be 1 foot behind the face of the curb. Only 2 mailboxes are permitted on 1 post. If more than 2 mailboxes are required, then set posts 3 feet apart for each set of double mailboxes. The post shall have a depth of 18-24 inches and in no instance shall the post be encased in concrete. Mailbox height shall be 38-44 inches from the edge of the pavement to the bottom of the mailbox.
DAMAGE POLICY: Mailboxes will only be replaced if the Wayne County Highway Department snowplow driver contacts the mailbox with the snowplow. However, mailboxes placed closer than 2 feet to the edge of the pavement will not be replaced if they are hit by the snowplow. Mailboxes damaged strictly by the force of the plowed snow will not be replaced. Authorized Highway Department personnel will determine if and when a mailbox gets replaced based on the above information. Only a standard issue aluminum mailbox and wood post will be used if replacement is necessary.
Mailbox Install.doc
http://www.wayne-county-engineer.com/documents/Mailbox Install.pdf