Emails are not read directly on the ISP, but downloaded to our hard disk for handling

One of the problems with html mail is that it usually is difficult to "download to your hard disk" for permanent storage. I don't see any indication (after only a brief look) that SeaMonkey has this capability.

HTML mail is downloaded to your machine for you to read, but ordinarily is stored only in your Temporary Internet Files folder, just like any other web page. The Temp Int folder is easily, and often automatically, erased, usually either when you close the browser and/or when you reboot.

John