Since version 12, Opera Mail for Windows allows external programs such as LibreOffice to send a file as a message attachment, but Opera Mail for Linux needs a third-party script to add this functionality for LibreOffice on Linux.
To get it working, do the following:
Insure that xautomation is installed.
Save the code with the name evolution. As of this writing, LibreOffice is hardcoded to recognize only a few mail clients by name. Opera isn’t on the list, but Evolution is. Make the script executable. I run a single user box and so placed it in my home directory, but on multiuser boxes /opt or /usr might be better locations.
Point LibreOffice to the script (Tools – Options – Internet – E-mail – E-mail program). Following my example, I pointed it to /home/USER/evolution. It is not necessary to restart LibreOffice.
To use, in LibreOffice open File – Send and select any relevant option (Document as email, Email as PDF, etc.). A message composition window will open in Opera Mail with the LibreOffice document attached in the format of your choosing.
Remember to add the script to your backup routine.
Many thanks to Joomis New Media for writing the script and making it available.