How to implement sending emails from wordpress site to ubuntu 14 server?

Question

postfix

Hello guys,
I looked through a bunch of English-language sites on this topic and, roughly speaking, got confused.
There is an ubuntu server with LAMP on board, virtual hosts are configured in Apache for several domains, in principle everything works. When there was only one site on the server, postfix was installed, after which messages from the forms were sent to the specified e-mail address.
After setting up virtual hosts, it all came to a head, which, in fact, is obvious.
How to properly and without crap set up sending emails to wordpress sites that are each under their own domain? There is a mail server, with boxes for each domain, in fact, letters will fall through there, though this is a completely different machine. Please tell me the solution, or direct what to read and study.
Thank you!
upd
__________________________
Let's say that postfix magically fixed itself and now all messages go to an external address.
What could be the reason that the message disappears on the way to the iredmail mail server?
1 server - sites, 2 server - mailer
According to the test results:
1 server - sends to external addresses gmail.com / yandex.ru, etc.
Server 2 - works in a regular two-way mode, transmits and receives mail from gmail / yandex
, there is a guess that somewhere the mail server does not like the address - and the antivirus kills the letter along the way. What do you suggest?

Answer 1

Initially, any smtp server (postfix, sendmail, exim) must be configured and running on your server.
You can check the sending of mail from the server console using the mail/mutt utilities.
Further, in order for each site (virtual host) to send mail on its own behalf, in the config of each apache virtual host, you must specify a directive with the domain name of this host:

php_admin_value sendmail_path "/usr/sbin/sendmail -t -i -f [email protected]"

Answer 2

sudo dpkg-reconfigure postfix
reconfigure postfix and everything should start working.