An SR-22 is a certificate from an Oregon-licensed insurance company certifying that you have purchased liability insurance that meets the minimum required limits of coverage (ORS 806.070 and 806.075).

The OR DMV requires that your insurance company file an SR-22 certificate with DMV if, for example:

• You failed to provide proof to DMV that you have liability insurance, 
• You’ve been convicted of driving without insurance,
• You’ve been involved in an uninsured accident,
• You are applying for a hardship or probationary permit, or
• At the time of reinstating your driving privileges following a DUII suspension.

It appears that Oregon State is requiring you to carry the SR-22 to reinstate your license after a DUII (Driving While Under the Influence of Intoxicants) suspension. According to the Oregon DMV, Oregon law requires you to keep a SR-22 in effect for 3 years from the ending date of a suspension which requires an SR-22 or for 3 years and 33 days from the date of a driving uninsured conviction. If you let it lapse for any reason, the insurance company must notify DMV and your driving privileges will then be suspended.

If your driving privileges have been suspended because you did not get an SR-22 certificate and you later get insurance, be sure you do not drive until an SR-22 certificate is on file with DMV and your driving privileges have been reinstated.

From this information, it would appear that you have to carry the SR-22 in order to keep your driving privileges. If you do not have a personal car of your own then you may need to get a non-owners SR-22 policy to fulfill the requirements.

As for your work mail truck, you will need to check with your employer's insurance provider as well as your own to make sure you are properly covered for driving it with your current situation. Insurance companies guidelines and terms of policies differ so that is why you will need to check with them to get a definitive answer.