phpmailer and gmail SMTP ERROR: Failed to connect to server: Network is unreachable (101) SMTP connect() failed

You might want to start by isolating this problem to determine whether it's truly a network problem; or whether it's specific to PHP mailer or your code. On your server, from a command prompt, try using telnet to connect to smtp.gmail.com on port 587, like so:

telnet smtp.gmail.com 587

You should see a response from smtp.gmail.com, like so:

Trying 173.194.74.108...
Connected to gmail-smtp-msa.l.google.com.
Escape character is '^]'.
220 mx.google.com ESMTP f19sm71757226qaq.12 - gsmtp

Do you see this, or does the connection attempt hang and eventually time out? If the connection fails, it could mean that your hosting company is blocking outgoing SMTP connections on port 587.

This worked for me:

change:

  $mail->SMTPSecure = 'ssl';
  $mail->Host = 'smtp.gmail.com';
  $mail->Port = '465';

to

  $mail->SMTPSecure = 'tls';
  $mail->Host = 'smtp.gmail.com';
  $mail->Port = '587';