To increase the upload size limit, edit the PHP configuration file.
If you using php7.4 then replace 8.1 to 7.4 in the below commands
sudo nano /etc/php/8.1/fpm/php.ini
Find the following line.
upload_max_filesize = 2M
Change the value like below. Note that this value should not be larger than the attachment size limit set by Postfix SMTP server.
upload_max_filesize = 50M
Then find the following line.
post_max_size = 8M
Change the maximum size of POST data that PHP will accept.
post_max_size = 50M
Save and close the file. Alternatively, you can run the following two commands to change the value without manually opening the file.
sudo sed -i 's/upload_max_filesize = 2M/upload_max_filesize = 50M/g' /etc/php/8.1/fpm/php.ini sudo sed -i 's/post_max_size = 8M/post_max_size = 50M/g' /etc/php/8.1/fpm/php.ini
Then restart PHP-FPM.
sudo systemctl restart php8.1-fpm
Nginx also sets a limit of upload file size. The default maximum upload file size limit set by Nginx is 1MB. If you use Nginx, edit the Nginx configuration file.
sudo nano /etc/nginx/conf.d/mail.example.com.conf
Add the following line in the SSL virtual host.
Save and close the file. Then reload Nginx for the changes to take effect.
sudo systemctl reload nginx
worked great, was really helpful.