Hi to all. Sorry for my english. I read all topics about attachments and couldn't find answer for my problem.
When I send a file more than 5 Mb RoundCube shows message "Unable to send message".
.htaccess conf file :
php_value upload_max_filesize 700M
php_value post_max_size 750M
php_value memory_limit 750M
logs/errors shows no error.
maybe your smtp server is limited not to accept messages greater than 5 mb? i have this limitation on my server. big attachments should be transferred by ftp and not by smtp.