hello, you're posting in the firefox support forum - firefox is a browser and doesn't handle your emails. in case you're using thunderbird as a mail client and have a question about it please say so, then we will move your question into the thunderbird queue. if you're accessing your mails through webmail, contact your email-provider in order to help you further...

Problems with email and how to find help

Yes, it's Thunderbird. I thought I had chosen that branch point. Sorry. Let's just say it's been a bad day!