1. You can configure MS Outlook to send and receive mails using either web.zmail.iitm.ac.in (visible in intranet as well as internet)  as your zimbra server. Provide your LDAP username and password as credentials without trailing 1 username.
2. Clients such as Mail on Apple iPad support zimbra. You can send / receive mails, use calendar and addressbook features of zimbra easily from both intranet as well as Internet. Use web.zmail.iitm.ac.in as your Zimbra server and provide your LDAP username and password as credentials.
3. A browser is all that you need to use the open web access (web interface) to send and receive mails. Use your LDAP username and password to login to the site.
4. Configure the incoming IMAP or POP3 server as web.zmail.iitm.ac.in and use LDAP username and password for the login credentials. Configure smtp2.iitm.ac.in or smpt.iitm.ac.in as outgoing smtp server and use your OpenLDAP username and password for the login credentials. Note that both servers uses authentication. Both these servers are visible from Internet. Eg., kmail or evolution on Linux, Thunderbird on Windows / Linux can be configured this way.
5. Attachment size incoming and outgoing is 10MB.
6. If none of the above options satisfy you, you can forward your mails on zimbra to your favourite email host. Mail to helpdeskeservices@iitm.ac.in to set the forward.
7. Total number of accounts as on 30/05/2024 : 1999