Ok, there are two issues:
If the Header "From:" contains only the email address (I had this problem with Roundcube):
The script doesn't work.
I already modified the script to check this problem.
Mails sent with nethtop 5 don't have the html signature applied:
It seemms a problem with altermime because the logo images are attached correctly
Watching the source mail generated by nethtop 5, the html source part, the tags that delimit the html source aren't present:
I tried to add manually to the source in the mail composition window of Nethtop (There's a button "Source Edit") but the changes aren't saved. If I reopen the "Source Edit" button, the changes are vanished:
Adding the parameter --force-for-bad-html to altermime, Nethtop seems to works too.
Outlook is a bit problematic with his imaginative interpretation of html code...
Link to new version here: