For instance, if you ever told Thunderbird how it should open a .patch file (eg. with TortoiseGit), you might find that, patches you send are no longer sent as inline text (
text/plain), but instead are sent as non-inline (
application/force-download). This can be a problem for people reading those patches with dumb e-mail clients, so you might be looking for a way to restore the inline behaviour.
Well, this is usually all handled in the
mimeTypes.rdfin your profile. For instance, to get a .patch file to always be sent as inline, you could ensure that you have the following entry:
<RDF:Description RDF:about="urn:mimetype:text/plain" NC:fileExtensions="patch" NC:description="Patch File" NC:value="text/plain" NC:editable="true">     <NC:handlerProp RDF:resource="urn:mimetype:handler:text/plain"/>   </RDF:Description>
In case this isn't enough, another parameter which you want to check is Tools → Advanced → Options → General Tab → Config Editor and then look for
mail.content_disposition_type. From what I understand, a value of 0 means that, anything that is not overridden in
mimeTypes.rdfwill be sent as inline. A value of 1 means that everything is sent as attachment, and a value of 2 means that everything, except images, is sent as attachment, so you probably want to have 0 there.