Adding the security code to config file breaks the test email

Thanks for the plugin.

I use Gravity Forms latest edition and most up-to-date WP version.

The plugin sends a test mail fine. Adding in the extra security lines of code to my config file makes it go pear-shaped. Comment it out and bingo! Test email works again.

Here is error message from in the plugin:

Versions:
WordPress: 4.9.5
WordPress MS: No
PHP: 7.0.1
WP Mail SMTP: 1.2.5

Params:
Mailer: smtp
Constants: Yes
ErrorInfo: SMTP connect() failed. https://github.com/PHPMailer/PHPMailer/wiki/Troubleshooting
Host: mail3.gridhost.co.uk
Port: 465
SMTPSecure: ssl
SMTPAutoTLS: bool(true)
SMTPAuth: bool(true)

Server:
OpenSSL: Yes
SMTP Debug:
2018-05-08 20:14:35 Connection: opening to ssl://mail3.gridhost.co.uk:465, timeout=300, options=array (
)
2018-05-08 20:14:35 Connection: opened
2018-05-08 20:14:35 SERVER -> CLIENT: 220 mail-lb-002.london.gridhost.co.uk ESMTP ready
2018-05-08 20:14:35 CLIENT -> SERVER: EHLO firkinsrealale.co.uk
2018-05-08 20:14:35 SERVER -> CLIENT: 250-mail-lb-002.london.gridhost.co.uk
250-SIZE 50485760
250-ENHANCEDSTATUSCODES
250-8BITMIME
250-DSN
250 AUTH PLAIN LOGIN
2018-05-08 20:14:35 CLIENT -> SERVER: AUTH LOGIN
2018-05-08 20:14:35 SERVER -> CLIENT: 334 VXNlcm5hbWU6
2018-05-08 20:14:35 CLIENT -> SERVER: bWFyY0BmaXJraW5zcmVhbGFsZS5jby51aw==
2018-05-08 20:14:35 SERVER -> CLIENT: 334 UGFzc3dvcmQ6
2018-05-08 20:14:35 CLIENT -> SERVER: eW91cl9wYXNzd29yZA==
2018-05-08 20:14:38 SERVER -> CLIENT: 535 5.7.0 Invalid email login [email protected] or password
2018-05-08 20:14:38 SMTP ERROR: Password command failed: 535 5.7.0 Invalid email login [email protected] or password
2018-05-08 20:14:38 SMTP Error: Could not authenticate.
2018-05-08 20:14:38 CLIENT -> SERVER: QUIT
2018-05-08 20:14:38 SERVER -> CLIENT: 221 2.0.0 Bye
2018-05-08 20:14:38 Connection: closed
2018-05-08 20:14:38 SMTP connect() failed. https://github.com/PHPMailer/PHPMailer/wiki/Troubleshooting