First - the Post Office is FEDERAL property. Access cannot be denied, if you've a certified service dog. Call one of your US senators or your US reprepresentative. THIS type of issue is why they have staffs! Ask for the info you need to allow the dog access w/o any problems in the future.
Second - IF your dog was just only a leash, HOW is anyone gonna KNOW it's a service dog? Here is a site to help you:
http://www.servicedogsamerica.org/ce...ion/index.html And:
http://www.servicedogsamerica.org/faq.html
It's not a big site? But a 'jacket' or the like sure can squelch problems before they occur. They also have some very good links to other resources.
I'll bet tho? IF you have that post offices' postmaster's name, and the post offices' phone # when [go the the US post office web site and you should get names from there...] talking to your congressmen or senators [hey call 'em all!] that that ENTIRE post office staff will be very quickly educated to this aspect of the ADA act!
Yes, this all mite take some time and local phone calls or e-mails? But, I'll bet that you have NO problems in the future!
Do let us know what all happens, please. - j