
The web client does what it should do. You can edit and send mails. High volumes of mails are no problem. Review collected by and hosted on G2.com.
IMAP: seems to be not working.
Outlook: close to impossible to get working.
iOS: hard to configure and intermittent time outs / slow downloads.
POP3: not supported.
Web client: it does not work on a small mobile screen.
Web client: having 10K of calendar items it takes 1 minute to load the calendar. Review collected by and hosted on G2.com.