The Postal Service's on-time performance is still only getting a "B" rating from its boss. But Postmaster General Anthony Frank says he is encouraged by the efforts being made.

"We don't want to be pretty good, we want to be excellent, but you have to start somewhere," Frank said in an interview.The latest results from an independent test of postal delivery found that more than three-fourths of the first-class mail arrived when expected.

The statistics for January through March, being released Monday, show that 79.9 percent of first-class mail scheduled for overnight delivery actually arrived that fast, down less than 1 percentage point from the previous quarter.

"We're coming along but we're still in the B's," said Frank. He said the agency seems to have a "high B in customer satisfaction and a low B in timeliness."