You can find pantheon-mail's data in ~/.local/share/pantheon-mail/. Inside this folder you'll find a folder for each email account. Inside each account folder you'l find an attachements folder, a geary.ini file, and a geary.db file. The geary.db file can be opened with any SQLite client. DB Browser for SQLite works great: sudo apt install sqlitebrowser. The ...
This feature seems to be not supported in current version of Pantheon Mail. I tested with embedded image and I can reproduce your problem.
However the current version of Geary 3.32 supports this (via right-click). Pantheon Mail was forked from Geary, if I'm not misteaken.
I would consider reporting this to elementary OS developers as a bug/feature request. ...
It can be accomplished with a standard e-mail signature that will be appended to the end of the e-mail message.
Here's how: go to Accounts (Ctrl+M), click the account you want the signature on, click the edit icon at the bottom, under the composer section check the box for "Sign e-mails", then fill in whatever you would like it to say, then click Save.
After making changes to desktop files manually, you often have to run:
This can also be pointed at your local user's desktop database like so:
And changes to mime types often need the following:
sudo update-mime-database /usr/share/mime
Although the update-mime-database ...