Ca. 2000. Converted a few companies (each around 20-30 mail / calendar users) from novell groupwise and ms exchange to notes/domino. Client OSes were windows 98, maybe even an occasional windows for workgroups. Not smooth sailing. Had to abort at least one conversion in the middle of the night because some "wizard" didn't work.

Users were trained in the new ways of email and some proprietary CRM app we developed, but IIRC at least half of the customers rolled back immediately because of user protest over user interface and missing/non-working functionality, one customer even went under.

In principle Lotus Notes was the best, but practically, it was horrible.