The gibberish we see there is typical of Thunderbird trying to show you contents of a message that it can't understand. And that may be because the indexing is messed up, and so it can't tell where one message ends and the next one begins. What you have shown us might, for instance, be an image, or a pdf document, or merely a (long!) email message encoded into one of the standard formats such as base-64. First, back up your profile. https://support.mozilla.org/en-US/kb/profiles-where-thunderbird-stores-user-data Then try repairing it. Select the affected folder, right-click, select '''Properties '''then '''Repair Folder'''. '''''Warning:''''' if your index is badly messed up, the messages might all disappear. At this point you might decide that restoring the backup and living with the mess is the least worst option. I don't know what to say about the "end of the day" part of it. Maybe you are getting real spam/junk and this time is when some user with an infected computer, in some other timezone, switches their machine on.