I have been asked to suggest a Vendor Overdue Report.  The report would need the Vendors name on it and include the PO numbers that were overdue, the line item details, the original due date and an area for a revised delivery date.  Then the report could be faxed to the vendor for them to fill in the revised delivery date and then fax it back.
 
We have quite a few customers that have a similar report that they fax to us.

I also found out from Mike that you can edit the RTM (both Evo and Classic) to force a page break between vendors so if you are going to print to paper and Fax you don't have to run separately for each vendor.
 
In Classic in the RTM Editor, click Reports - Groups and there is a setting for "On Group Change Start new Page" that will force a page break between vendors if you run the report sorted by vendor.
 
In Evo, move to the tab of the desired subreport and then you can click Report - Groups and set the "Start new Page" setting.