Sobre os servidores de e-mail Postfix e Zimbra, seguem-se tr...

Postfix / QMAIL – Servidores SMTP

É uma implementação de serviço de correio eletrônico em ambiente Linux e Unix. Alternativa I errada

II E III  correta

"Postfix runs on AIX, BSD, HP-UX, IRIX, LINUX, MacOS X, Solaris, Tru64 UNIX, and other UNIX systems. It requires ANSI C, a POSIX.1 library, and BSD sockets"

Fonte: http://www.postfix.org/features.html

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"Zimbra Desktop is a free and open source email client application that gives you online and offline access to all your email accounts in one place. It’s cross-platform, available on Windows, Mac OS and Linux"

fonte: https://www.zimbra.com/zimbra-desktop/

O Zimbra aceita os três itens citados.

Windows sendmail

The Zimbra Server uses several open source projects (see the section, Included open source projects). It exposes a SOAP application programming interface to all its functionality and is also an IMAP and POP3 server. The server runs on many Linux distributions.[13] On other, non-Linux operating systems it can be run using a virtual machine and using container technology. It supports CalDAV, CardDAV and SMTP for messaging, LDAP for directory services, and Microsoft Active Directory (AD).

https://en.wikipedia.org/wiki/Zimbra