Lotus Notes is IBM’s mail client, whose respective server is Lotus Domino. The reason for its popularity is its high-tech security, which is very useful for today’s internet users. Lotus Notes saves its mailboxes in NSF format, which you can read only in Notes, no other email client. But in recent years it has started to lose its popularity among users that’s due to its complex interface & navigation.
It is observe that many users are favoring Zimbra Web Client over Lotus Notes, as it offers equivalent security but has a very simple interface. One of the possible option to open and save Lotus Notes emails in zimbra is this zimlet - EML to Zimbra Converter.
Well if you drag & drop emails from Lotus Notes & save in a lock folder in your machine, you will see the files are in .eml format, then use EML to Zimbra Converter available, which will convert the Lotus Notes eml files into Zimbra TGZ format & once that done you can import the tgz file into Zimbra and can access emails in Zimbra.