I have been using this product since last 4 years now, we are running our project with mail nest very successfully over there.
they provide excellent customer support team which always help us whenever required so far no issues of any sort from their side or anything else that i can think about as well! The best part will be when you guys read my comment then it's like your first mistake was mine rather than theirs if only everyone would give such good reviews after usage :) We use them both internally & externally at projects/services level too where large number users access emails via web applications (both desktop clients + mobile). They offer multiple features including multi inbox management etc., along great UI / UX design approach also - easy navigation through menus makes user friendly products really useful even though its not cheap but worth every penny spent by paying customers!