Cannot receive account setup email notification

[blueberry]

hi, i tried to create a few accounts in Vestacp, but couldn't receive any email notification. I created a php web form, but did not receive any email via php sendmail function as well. In fact, the VestaCP installation, i did not receive the initial email as well.

Setup is using Dynamic DNS, Portforwarding all configured (Eg. Port 25, 21, 22... FTP, SSH all working).

I tried to install sendmail function, but still did not work. Can anyone advice?

sudo nano /etc/mail/local-host-names
domain-name.com
machine_name.domain-name.com

sudo nano /etc/hostname
127.0.0.1 localhost
192.168.0.X machine_name.domain-name.com machine_name

192.168.0.X is the internal LAN fixed IP address of the machine.

set sendmail_path in php.ini
sendmail_path = /usr/sbin/sendmail -t -i -f [email protected]

I could not find where to change this email address: ubuntu_username@machine_name . Is this the cause?

Ubuntu 16.04.
-----

050 550-Verification failed for <ubuntu_username@machine_name>
050 550-The mail server could not deliver mail to ubuntu_username@machine_name. The account or domain may not exist, they may be blacklisted, or missing the proper dns entries.
050 550 Sender verify failed
050 503-All RCPT commands were rejected with this error:
050 503-Sender verify failed

[blueberry]

Exim4 not working for me, grey out in the Vestacp control panel, can't start as well, hence wanted to see if sendmail works as an alternative.

[blueberry]

Tried again, purge sendmail, re-install exim4. Now exim4 finally shows up activated in VestaCP, however, am still unable to receive email notifications on new account/ new database creation. PHP forms to emails are not working as well. Any clue or advice? Would greatly appreciate.

[blueberry]

I'm happy to inform that after hours of read-ups and testings, i managed to get Exim4 working again. Ran dpkg-reconfigure exim4-config and email notification finally works now!