After installing the server, how can I add a username and password?

[SevenN]

After installing the server, how can I add a username and password?
Do I need to install additional software to create a username and password? I can't seem to find them.

[SevenN]

I keep receiving a message that IMAP connection is failing.

[Dmitry42]

Roundcube - its just web-based maill client.

So you must install IMAP, SMTP server and create on it users accounts.

[SevenN]

Hello, are you asking for recommended IMAP and SMTP servers? Some popular options include Kolab, Mail-in-a-Box, iRedMail, and Mailcow.

[Dmitry42]

No - I answer to your question about creating new login.

Creating new user login depend from your server. You can store users in Database, OS, LDAP, AD and etc.