Today Mailtrain got support for attaching files for campaigns. To add new attachments click on the “Edit Campaign” button and once in the edit view you should see a new tab “Attachments”. On that page you can upload, view and delete attached files.
Once you send out the campaign, all listed files are added as normal attachments to the messages.
Be aware that Mailtrain has maximum POST body defined in the configuration file (postsize option) that defaults to 2 MB. If your attachment is larger than the allowed post size, then the upload will fail.