Hey everyone, long time lurker, first time posting.

Having some difficulties understanding the basics of setting up emails for my websites. On my old droplet I'm using a control panel, though I'm trying to optimise and put it all on the new server. Seeing as I had quite a long period of troubleshooting to set up the last thing I tried to do, I thought I'd get advice before running in.

Basics:

Ubunto 14.04 with LEMP

running 3 sites so far:

• site1.com
• site1.com/blog (wordpress)
• site2.com (wordpress)
• site3.com
• (site 4 is not hosted on this droplet)

Would like to have:

7 email addresses on site 1
1 email address on site 2
1 email address on site 3
4 email addresses for site 4
Roundcube or similar Webmail that can access any site (or just site 4 if it's too complicated)

primarily that forward to gmail and can be responded from gmail (I'm familiar with setting up aliases on gmail settings and adding the MX records to the DNS)

What I'm looking to learn:

What I need to get basic emails addresses up - I imagine it's this tutorial:

https://www.digitalocean.com/community/tutorials/how-to-configure-a-mail-server-using-postfix-dovecot-mysql-and-spamassassin

or maybe just this one?

https://www.digitalocean.com/community/tutorials/how-to-install-and-setup-postfix-on-ubuntu-14-04

and

The simplest way to set up roundcube webmail so ideally any site can access their mails online. (or just site4 if it's too hard to get them all)

Thanks in advance, you amazing minds!