unable to write the emails to the inbox

I have multiple problems with Mozilla and Thunderbird 1. when I attempt to attach a jpg image (about 25 kb), it never attaches it to the document. 2. my primary problem is the message in the question "Error with account Bob's email + "Unable to write the email to the mailbox. Make sure the file system allows you write privileges and you have enough disk space to copy the mailbox". I have compacted all of the mail boxes and don't know what else to do. 3. I have been unable to sign onto my Mozilla account and after requesting a reset of the password, the enabling email which has supposedly been sent to both of my email addresses. https://essayacademia.com

I had the same problem on my site https://topwritingcompanies.com/, for email admin@topwritingcompanies.com

I've found the problem after some hard debugging:

On my previous installation of Thunderbird the default mail store was Maildir for some or other reason, and the new installation was default set to mbox, so when creating a new account it was set to mbox, and if the whole global inbox in maildir then it cant store mails as mbox which then bombed out. By setting the default mail store to maildir on the new installation, then all started to work.