For Drupal 8 Install PHPMailer and SMTP:
Go to the root of your Drupal 8 project and execute below to install and enable smtp module from Admin interface or via drush
composer require phpmailer/phpmailer
composer require drupal/smtp
Configure SMTP at: /admin/config/system/smtp
INSTALL OPTIONS
Set SMTP as the default mailsystem
On
When on, all mail is passed through the SMTP module.
SMTP SERVER SETTINGS
SMTP server
smtp.host.name
The address of your outgoing SMTP server.
SMTP backup server
The address of your outgoing SMTP backup server. If the primary server can't be found this one will be tried. This is optional.
SMTP port
25
The default SMTP port is 25, if that is being blocked try 80. Gmail uses 465. See
http://gmail.google.com/support/bin/answer.py?answer=13287 for more information on
configuring for use with Gmail.
Use encrypted protocol
No
This allows connection to an SMTP server that requires SSL encryption such as Gmail.
Enable TLS encryption automatically
On
Whether to enable TLS encryption automatically if a server supports it, even if the
protocol is not set to "tls".
Timeout
60
Amount of seconds for the SMTP commands to timeout.
Turn on the SMTP keep alive feature
Enabling this option will keep the SMTP connection open instead of it being openned
and then closed for each mail
SMTP AUTHENTICATION
Leave blank if your SMTP server does not require authentication.
Username
SMTP Username.
Password
SMTP password.
If you have already entered your password before, you should leave this field blank, unless you want to change the stored password. Please note that this password will be stored as plain-text inside Drupal's core configuration variables.
E-MAIL OPTIONS
E-mail from address
The e-mail address that all e-mails will be from.
E-mail from name
The name that all e-mails will be from. If left blank will use a default of: Portal
Name . Some providers (such as Office365) may ignore this field. For more
information, please check SMTP module documentation and your email provider
documentation.
Allow to send e-mails formatted as HTML
Checking this box will allow HTML formatted e-mails to be sent with the SMTP protocol.
SMTP CLIENT SETTINGS
Hostname
[email protected]
The hostname to use in the Message-Id and Received headers, and as the default HELO
string. Leave blank for using _.
HELO
Test
The SMTP HELO/EHLO of the message. Defaults to hostname (see above).
SEND TEST E-MAIL
E-mail address to send a test e-mail to
Type in an address to have a test e-mail sent there.
Enable debugging
Checking this box will print SMTP message
Enabling Debugging will help know the SMTP isssues, check the project page for other error refrences: https://www.drupal.org/project/smtp