It is maybe too much I'm asking for but anyway I'll try it. Is there a way to filter users' access to their mailboxes based on account and IP adress? For example:
user1 can access his mailbox from local subnets only
user2 can access his mailbox from local subnets and/or another specified public IP
user3 can access his mailbox from everywhere
Why would I want this? Most of my users for sure do not need to access their mailboxes when out of office. Some of them are at remote location (with static IP) and so they need access just from their IP and rest of them are travelling a lot and need access from everywhere. When I open POP3/IMAP/HTTPS at firewall it is for everyone and there are some security concerns. Even when "secure ports" are used so passwords exchange is protected, there is no protection when attacker tries to guess users' password and succeeds. If only selected account were accessible from the outside, the risk would be lower.