500 server error in Laravel mail send

My .env file looks like the below configuration. When I send mail it shows a 500 server error. It works fine in local xampp server (where APP_ENV=local). There is no error shown in log file also, but when I change the option:

'pretend' => true, 

then log file write some text like

production.INFO: Pretending to mail message to: sales@accezatech.com

Can anyone help me please to find where I made a mistake?

APP_ENV=production
APP_DEBUG=true
APP_KEY=DDPTFVZSt4zikAZXZEp7Z0bebKQA1Mug

DB_HOST=localhost
DB_DATABASE=ferdosh_acceza_db
DB_USERNAME=ferdosh_dbuser
DB_PASSWORD=**********

CACHE_DRIVER=file
SESSION_DRIVER=file
QUEUE_DRIVER=sync

MAIL_DRIVER=smtp
MAIL_HOST=mail.accezatech.com
MAIL_PORT=26
MAIL_USERNAME=visitor@accezatech.com
MAIL_PASSWORD=********

via Chebli Mohamed