As Lyndon said, the proof that it works well is in the existence of multiple implementations in which it works well.
And for the record, I have participated in interoperability tests with a number of servers. Those that have proven themselves include: UW, Cyrus, and MessagingDirect. Others have passed as well, but the above are the ones I have first hand knowledge of (at the source code level). They all implement all of 2060, let alone 3501. There are no excuses.
--lyndon
